Chinese gold medallist swimmer Ye Shiwen, 16, has denied taking drugs to enhance her performance, saying there was "no problem with doping".
A US coach earlier said Ye's record-breaking performance in Saturday's 400m individual medley was "disturbing".
Elsewhere, police are investigating an allegedly offensive tweet sent to UK diver Tom Daley about his late father.
Meanwhile, Team GB will be going for medals in events including canoeing, diving and equestrian.
Zara Phillips will be one of those taking part in the showjumping finale of the eventing competition, with Team GB going into the final day in the silver medal position.
Team GB will also be competing in football, rowing, gymnastics and sailing, while the athletics team will arrive at the Olympic Village after attending a training camp in Portugal.
'Firm policy' on dopingYe Shiwen took seconds off her personal best to break the world record and win a gold medal in the 400m medley on Saturday, swimming faster in the last 50m than the winner of the men's event.
John Leonard - the executive director of the World Swimming Coaches Association - said her performance was "unbelievable".
But Ye Shiwen said: "There is no problem with doping. The Chinese team has a firm policy so there is no problem with that."
All medal winners at the Olympics are automatically drug-tested.
Meanwhile, Dorset Police have said they are looking into a Twitter message that was sent to diver Tom Daley, after he failed to win a medal in the synchronised diving event on Monday.
The tweet is said to have made reference to his father, who died of cancer in May last year.
Team GB medallistsOn Monday, Team GB's men's gymnasts won bronze - the country's first team medal in the sport in 100 years.
They had initially won silver, but were demoted after fourth-place Japan successfully challenged the result, moving up to silver.
UK Sport chief executive Liz Nicoll said Team GB had made a good start.
"We want more medals than Beijing so at least 48 medals in at least 12 sports, that's the official target for the outcome from these games," she said.
"Three fantastic medals, the bronze medal from the men's team gymnastics was outstanding, that's a moment in history, that was not predicted."
Games organisers Locog put more Olympic tickets on sale overnight but will not confirm the details of the latest release until a media conference later on Tuesday.
It is making seats available day-by-day after criticism of empty seats which had been allocated to sports federations.
The tickets can be bought only online, before they are picked up at collection points in venues for pre-purchased tickets.
In other Olympic developments:
- The women's volleyball team won Team GB's first-ever Olympic victory in the sport, beating Algeria at 00:37 BST on Tuesday
- In hockey, Team GB's men opened their campaign with a 4-1 thrashing of Argentina
- Britain's Liam Tancock missed out on a medal in the the men's 100m backstroke final
- Lithuanian 15-year-old Ruta Meilutyte - who goes to school in Plymouth - won her country's first ever Olympic gold in the swimming pool in the women's 100m breaststroke
- Transport for London said the transport system ran smoothly on the first full working day of the Games
