- NEW: At least 21 people are killed across Syria on Saturday, opposition activists say
- NEW: Syria says armed forces killed and injured "terrorists" during clashes in Aleppo
- The U.S. secretary of state will visit Syrian opposition and Turkish leaders Saturday
- Syrian state media: Terrorists are responsible for the abduction of journalists
Aleppo, Syria (CNN) -- Two longtime opposition strongholds took a beating by Syrian forces on Saturday, with troops storming the areas of Daraa and Homs, opposition activists said.
In Daraa, the birthplace of anti-government protests, shelling killed at least three people, the opposition Syrian Observatory for Human Rights said.
And in the Daraa suburb of Tafas, the Syrian army invaded the city "amid intense gunfire," said another opposition group, the Local Coordination Committees of Syria. The LCC said a woman and her fetus "were martyred in the delivery unit in Tafas Hospital due to shelling."
Reports of carnage also emerged from the devastated city of Homs, which had been a hotbed of anti-government sentiment that sustained weeks of incessant attacks earlier this year.
Across the country, at least 21 people were killed in violence early Saturday, the LCC said. Seven were reportedly killed in Aleppo, Syria's largest city and a key battleground for regime and rebel fighters.
Syrian state-run TV proclaimed success against "armed terrorist groups" in Aleppo, saying "our armed forces managed to kill and injure a number of these terrorists in these clashes."
U.S. Secretary of State Hillary Clinton will meet with Syrian opposition and Turkish leaders in Istanbul on Saturday to discuss the spiraling Syrian crisis.
But even after a fresh wave of U.S. sanctions against President Bashar al-Assad's regime and Britain's announcement of new aid for Syrian rebels, the civil war continues unabated.
On Friday, the United States announced new sanctions Friday against Syria and its supporters, focusing on Hezbollah's support for the regime and a Syrian oil company for violating U.S. sanctions on Iran.
The U.S. State Department sanctioned the refiner Sytrol for selling $36 million of gasoline to Iran in April.
Earlier Friday, the U.S. Treasury Department announced an extension of sanctions against Hezbollah, a Lebanon-based Shiite militant group, for its support of the Syrian government.
Hezbollah, which the United States has designated a terrorist organization supported by Iran, has provided training, advice and extensive logistical support to President Bashar al-Assad's military campaign against an uprising that began in March 2011, the department said.
A Free Syrian Army fighter aims an RPG as he waits for Syrian Army tanks in the Salaheddine neighborhood of central Aleppo on Friday, August 10. 
A Free Syrian Army fighter walks on an empty street in the Salaheddine neighborhood. 
Free Syrian Army members check a confiscated cache of weapons found on a truck that was searched at a checkpoint in Dana. 
A rebel fighter fires an anti-aircraft gun during a regime airstrike on Tel Rafat, a village north of Aleppo, on Thursday, August 9. The Syrian government and rebel groups have been battling for control of Aleppo, a key front in the conflict that has morphed into a civil war. 
A Syrian air force fighter plane fires during an airstrike Thursday in Tel Rafat, north of Aleppo. Forces loyal to the regime have been shelling Aleppo, Syria's largest city. 
A truck burns after apparently being hit by rockets during an airstrike on Tel Rafat. 
Men carry the body of a boy killed in an airstrike in the village of Tel Rafat. 
A boy's body is uncovered in the rubble of a house demolished during the recent clashes in Tel Rafat. 
A man steps on a carpeted image of Syrian President Bashar al-Assad in Anadan, northwest of Aleppo, on Wednesday, August 8. The fighting has taken a toll on al-Assad's regime, which has been hit by assassinations and political and military defections. 
Residents sift through rubble Wednesday searching for bodies under a collapsed house destroyed in an airstrike. 
Syrian refugees bathe Wednesday at Al Zaatri U.N. camp in the Mafraq, Jordan, near the border with Syria. The recent shelling has led thousands of residents to flee Syria. 
Syrian refugees cook a meal at Al Zaatari camp in Mafraq, Jordan. 
A Syrian rebel prepares his weapon as a group of Free Syrian Army fighters head toward the fighting with Syrian Army soldiers in the Salah ad-Din neighborhood of central Aleppo on Sunday, August 5. 
Syrians evacuate a civilian wounded in shelling in the northern city of Aleppo on Saturday, August 4. Syria's armed forces pounded Aleppo's rebel-held Salah ad-Din district with air and ground fire as violence also raged in the Shaar and Sukkari districts, according to reporters in the area and a rebel commander. 
A vehicle burns as Syrians walk through debris from clashes between Syrian armed forces and rebels in the northern city of Aleppo on Saturday, August 4. 
A boy plays on the gun of a destroyed Syrian army tank partially covered in the rubble of the destroyed Azaz mosques, north of the restive city of Aleppo, on Thursday, August 2. 
Smoke rises from Al-Safsaf in Homs on Friday, August 3. 
A boy plays with an AK-47 rifle owned by his father in Azaz, some 29 miles north of Aleppo on Friday, August 3. 
Syrians climb on an abandoned Syrian army tank north of Aleppo on Thursday, August 2. 
A man looks at a destroyed Syrian army compound in Azaz, 29 miles north of Aleppo on Friday, August 3. 
A Syrian refugee walks at the Al Zaatri refugee camp in the Jordanian city of Mafraq, near the border with Syria, on Friday, August 3. 
People and a member of the Free Syrian Army commute on Wednesday, August 1, past a building on the outskirts of Idlib that was hit by rocket fire Tuesday night by forces loyal to President Bashar al-Assad. Unrest spread across other volatile regions of the country as al-Assad's forces shelled targets and launched raids in and around Damascus, Homs, Daraa and Deir Ezzor. 
A woman and child on Wednesday walk through rubble of a building destroyed by shelling from forces loyal to Syrian President Bashar al-Assad in Aleppo. 
Demonstrators hold an opposition flag during a protest Wednesday against Syria's President Bashar al-Assad in Damascus. 
Syrian girls on Wednesday walk past a Syrian army tank captured two days earlier by rebel fighters at a checkpoint in the village of Anadan. The strategic checkpoint secures the rebel fighters free movement between the northern city of Aleppo and Turkey. 
Rebel Free Syrian Army fighters capture a policeman who they allege is a "Shabiha" or pro-regime militiaman, on Tuesday, July 31, as the rebels overrun a police station in Aleppo. 
Rebel fighters load an anti-aircraft machine gun on an armored vehicle in Atareb, east of Syria's second-largest city, Aleppo, on Tuesday, July 31. 
Syrian boys run near a building hit by bullets and fire in Atareb. 
A member of the Free Syrian Army fires at forces loyal to President Bashar Al-Assad in a district of Aleppo called Salah Edinne on Tuesday. 
A member of the Free Syrian Army carries an injured civilian to safety in Aleppo's district of Salah Edinne on Tuesday. 
Members of the Free Syrian Army learn that a tank belonging to forces loyal to President Bashar Al-Assad is heading to the area. 
A Syrian boy carries bags of bread as people wait outside a bakery near Syria's second-largest city, Aleppo. 
A photo released by Syrian Arab News Agency depicts damaged buildings in Homs on Monday, July 30. 
A Free Syrian Army fighter takes position Sunday, July 29, in Aleppo as people flee shelling. Intense clashes have been under way for more than a week between the regime and rebels in Aleppo, Syria's commercial and cultural center. 
Parts of Syria's largest city saw the fiercest clashes yet in the country's 16-month crisis on Saturday, July 28. About 200,000 people have fled fighting in Aleppo and surrounding areas in the past two days, a U.N. official says. 
Fighting leaves vehicles damaged Saturday in the southwestern city of Daraa. 
Syrians carry the body of a man allegedly killed in the bombardment of Sukari, southwest of Aleppo, by Syrian regime forces on July 27. 
Destruction appears widespread in Homs on Friday, July 27, in a handout photo from the Syrian opposition Shaam News Network. 
A Syrian opposition fighter takes aim during clashes with forces loyal to President Bashar al-Assad in Aleppo on Wednesday, July 25. 
Family and friends mourn over the body of Usame Mircan, who they say was killed by a Syrian government sniper in Aleppo on Wednesday. 
Usame Mircan's mother grieves after he was killed during fighting in Aleppo. 
The bodies of men killed during clashes between Syrian rebel fighters and goverment forces lie on the Aleppo street on Thursday, July 26. 
Fighters from the Syrian opposition rest at a former primary school in Aleppo on Wednesday. 
Residents take cover as fighters from the Syrian opposition clash with forces loyal to President Bashar al-Assad in Aleppo on Wednesday. 
Syrian rebels guard a checkpoint in Aleppo on Wednesday. 
A damaged portrait of President Bashar al-Assad sits among piles of debris at a checkpoint manned by Syrian rebels in Aleppo on Wednesday. 
Syrian rebels drive through Selehattin near Aleppo during clashes with government forces on Monday, July 23. 
A Syrian rebel runs through the streets of Selehattin during an attack on a municipal building. The rebel Free Syrian Army says it is attempting to "liberate" several districts of Aleppo. 
Syrian rebels work to find snipers during clashes Monday between the opposition and government forces in Selehattin. 
Syrian rebels make their way down a street Monday in Selehattin near Aleppo. If they gain control of Aleppo, it would mark a pivotal point in the Syrian crisis. 
Syrian rebels take cover behind sandbags during fighting Monday at the entrance to the city of Selehattin. 
On Sunday, July 22, a Syrian refugee looks out from a bus as he arrives at a refugee camp in Turkey opposite the Syrian commercial crossing point Bab al-Hawa. 
Syrian refugees flee from a refugee camp nicknamed "Container City" on the Turkish-Syrian border in Kilis province, southern Turkey, on Sunday. 
Smoke from artillery shelling rises above Jbatha Al-khashab. 
An armed Syrian rebel wearing the jersey of FC Barcelona rests with comrades near the northern city of Aleppo on Sunday. The rebel Free Syrian Army announced the start of the battle to "liberate" Aleppo, Syria's commercial hub and a traditional bastion of President Bashar al-Assad's regime. 
In this photo released by the Shaam News Network, a truck burns after shelling in the Erbeen suburb of Damascus on Saturday, July 21. 
Refugees fleeing the violence in Syria arrive by bus in Baghdad, Iraq, on Saturday. 
Turkish soldiers stand guard at the Cilvegozu border gate in Reyhanly that connects to Syria's Bab al-Hawa post. An estimated 120,000 people have fled Syria to Turkey, Iraq, Lebanon and Jordan. 
Burned-out trucks at the Bab al-Hawa Syrian border post with Turkey on Friday, July 20. Syrian rebels seized control of the post after a fierce battle with Syrian troops, an AFP photographer at the scene reported. 
Syrian soldiers celebrate in the al-Midan area in Damascus on Friday. Syrian regime forces routed rebel fighters from the Damascus neighbourhood of Midan, Syrian state television reported, saying troops had "cleaned" the district of "terrorists." 
Journalists are shown a dead body on a government tour of the al-Midan area in Damascus on Friday. 
Members of Syria security forces rest in the al-Midan area in Damascus on Friday. 
Syrian army soldiers hang their national flag in a partially destroyed neighborhood in the al-Midan area in Damascus. 
Smoke hangs in the air in a partially destroyed neighborhood in the al-Midan area in Damascus. 
Members of Syria security forces pose for photographers in the al-Midan area in Damascus after driving out the rebel fighters. 
Syrian residents take goods from a truck that rebels captured at the Bab al-Hawa border crossing with Turkey on Friday. 
A picture released by the official Syrian Arab News Agency on July 19 shows Syrian General Fahd al-Freij meeting with President Bashar al-Assad in Damascus after his swearing-in ceremony as defense minister. 
A man holds up a picture of President Bashar al-Assad at a former police station in Atareb after clashes between Syrian soldiers and Free Syrain Army near Aleppo on Thursday, July 19. Rebels seized control of border crossings with Iraq on Thursday, dealing a new blow to al-Assad, as China and Russia dismayed the West by blocking U.N. action against his regime. 
People walk along the street in Atareb amidst damage caused by clashed between Syrian soldiers and the Free Syrian Army. 
A Syrian man checks the former police station of Syrian regime after a clash at Atareb on Thursday. 
Smoke ascends from from alleged shelling of the Syrian village of Jebata al-Khashab as seen from the hill village of Buqaata in the Israeli-annexed Golan Heights on Thursday. 
The death toll in Syria on July 12 reached 287, making it the bloodiest day in Syria since the uprising began. As it has done consistently, Syrian state television blamed "armed terrorist groups" for the killings. 
A Syrian woman sits with her grandson outside a damaged building after attacks in the Syrian village of Treimsa on July 13, 2012. More than 200 people were massacred in the town, according to activists. 
A Syrian demonstrator holds an opposition flag during a protest in Damascus on July 2, 2012. There have been increasing reports of violence in the Syrian capital. 
Syria's President Bashar al-Assad waves as he arrives for a speech to Syria's parliament in Damascus on June 3, 2012. The embattled president denied that government forces were behind the "outrageous" massacre in Houla. 
People gather at a mass burial on May 26, 2012 for victims reportedly killed during an artillery barrage from Syrian forces in Houla. The attack left at least 108 people dead, including nearly 50 children, according to the United Nations. 
Members of the Free Syrian Army return to Qusayr on May 12, 2012 after an attack on Syrian regime forces in the village of Nizareer, near the Lebanese border in Homs. 
A U.N. observer speaks with Syrian rebels and civilians in the village of Azzara on May 4, 2012, days before the country's parlianemtary polls were held against a backdrop of unrest. 
Thousands of Syrians wave their national flag and hold portraits of President Bashar al-Assad and Lebanon's Hezbollah chief Hassan Nasrallah, right, during a rally to show support for their leader on March 29, 2012 in Damascus. 
Syrian rebel fighters man a checkpoint leading into the town of Taftanaz in the rebel stronghold province of Idlib on March 20, 2012. 
A Free Syrian Army rebel mounts his steed in the Al-Shatouria village near the Turkish border in northwestern Syria on March 16, 2012, a year after the uprising began. The Free Syrian Army is an armed opposition group made up largely of military defectors. 
Syrian refugees walk across a field before crossing into Turkey on March 14, 2012. International mediator Kofi Annan called for an immediate halt to the killing of civilians in Syria as he arrived in Turkey for talks on the crisis. 
A day after the twin suicide bombings, Syrian mourners pray over the coffins of the 44 people killed during a mass funeral in Damascus. 
A Syrian man who was wounded in a suicide attack rests at a hospital in Damascus on December 23, 2011. Suicide bombers hit two security service bases in the Syrian capital, killing dozens of people. 
Arab foreign ministers attend an emergency meeting at the Arab League headquarters in Cairo on October 16, 2011, to discuss the crisis in Syria. 
U.S. Secretary of State Hillary Clinton speaks to the media in Washington on August 18, 2011. Clinton said U.S. sanctions on Syrian oil "strike at the heart of the Syrian regime." 
Syrian youths wave national flags while army troops drive out of Daraa on May 5, 2011. During a week-long military lockdown of the town, dozens of people were reportedly killed in what activists described as "indiscriminate" shelling on the city. 
Syrians in Damascus protest in the street on March 25, 2011, after clashes with government forces in Daraa left several dead. 
Supporters of Syrian President Bashar al-Assad rally on April 1 in Istanbul, Turkey, as delegates from dozens of countries gather to push for ways to end the deadly violence in Syria. The United Nations estimates more than 10,000 people have been killed since the beginning of the crisis in March 2011. The conflict is now being labeled a civil war by the International Committee of the Red Cross. 
Photos: Showdown in Syria 
British aid for Syrian rebels 
Watch reporter dodge danger in Syria 
Photos capture intense Syria images 
Can Syria cause Mideast to destabilize? The agency accused the group of training Syrian government personnel inside Syria, and facilitating the training of Syrian forces by the Quds Force, an elite unit of Iran's Revolutionary Guard Corps.
"Hezbollah's extensive support to the Syrian government's violent suppression of the Syrian people exposes the true nature of this terrorist organization and its destabilizing presence in the region," David S. Cohen, under secretary for terrorism and financial intelligence, said in a statement.
Al-Assad's inner circle: Mostly family, like 'mafia'
Also Friday, Britain announced $7.8 million more aid for the Syrian rebels.
The money is not intended for weapons, but for medical and communication supplies, British Foreign Secretary William Hague said.
"The people of Syria cannot wait indefinitely," he said.
Syrian rebels arrested a number of pro-regime journalists while they were covering military operations in al-Tal, a suburb of Damascus, according to the Syrian Observatory for Human Rights.
Syrian state-run media reported that a crew from Al-Ikhbariya TV, which is pro-regime, had lost communication with their office and that "armed terrorist groups and countries that are supporting them" are to be held responsible.
Roughly 17,000 people have been killed since the fighting began, the United Nations said last month. Opposition activists have put the toll at more than 20,000.
Two days in Aleppo: Guns, graveyards and stairwell beds
The bloodshed has prompted increasing numbers of Syrians to flee into Turkey, Lebanon, Jordan and Iraq, the United Nations refugee agency said Friday.
Almost 150,000 Syrians are now living as refugees, the agency said.
What does Iran get for supporting al-Assad?
In Turkey alone, the refugee population has exceeded 50,000, with more than 6,000 new arrivals -- many from the Aleppo area -- this week.
CNN's Saad Abedine, Jamie Crawford, Lesa Jansen, Ivan Watson and Holly Yan contributed to this report.
