Rupert Murdoch called Tony Blair urging him not to delay the invasion of Iraq, former Number 10 communications chief Alastair Campbell has said.
The claim is made in the latest part of Mr Campbell's diaries, which are being serialised in the Guardian newspaper.
Mr Campbell said there were three calls in March 2003, a week before a crucial vote on Iraq in the House of Commons.
There has been no response to the claims from Mr Murdoch's company, News Corporation, or Mr Blair's office.
'Over-crude diplomacy'According to Mr Campbell's book, The Burden of Power: Countdown to Iraq, Mr Murdoch's moves were made to support Republicans in Washington.
The ex-Downing Street director of communications said the interventions from Mr Murdoch came "out of the blue".
In one call Mr Murdoch was said to have tried to pressure the then Prime Minister Mr Blair to accelerate UK military involvement in Iraq.
On 11 March 2003, Mr Campbell wrote that Mr Blair "took a call from Murdoch who was pressing on timings, saying how News International would support us, etc".
Mr Campbell continued: "Both TB [Tony Blair] and I felt it was prompted by Washington, and another example of their over-crude diplomacy. Murdoch was pushing all the Republican buttons, how the longer we waited the harder it got."
The following day he added: "TB felt the Murdoch call was odd, not very clever."
Withdraw supportMr Murdoch has previously told the Leveson Inquiry into press standards that he had "never asked a prime minister for anything".
But earlier this week Sir John Major said at the inquiry that Mr Murdoch had pressed him on policy when he was prime minister in the mid 1990s.
Sir John said the media magnate asked him to change the Conservatives' stance on Europe otherwise his papers would withdraw their support.
Sir John recalled the exchange from a private meeting in 1997, which he said he had not spoken about before.
Later that year his Conservative party lost power to Labour with the Sun backing his rival Mr Blair.
