The government's director of communications, Alastair Campbell, a key aide of Prime Minister Tony Blair, wrote to the BBC earlier, asking whether it stood by its reports and demanding a reply by the end of the day.

BBC director of news Richard Sambrook promptly fired back, saying "in my experience, this is an unprecedented level of pressure on the BBC from Downing Street.

"The BBC will respond properly to these matters, but not to a deadline dictated by Mr Campbell," Sambrook said in a statement, adding that the broadcaster stood by its stories.

The stand-off follows an attack on the BBC Wednesday by Campbell, known as the "sultan of spin" for his skill in manipulating the media.

Appearing before parliament's foreign affairs committee, Campbell said that there was no truth to a BBC radio report, quoting an unnamed source, that Blair's office embellished a September 2002 dossier on Iraq to make the threat posed by Saddam Hussein appear greater.

"In relation to the BBC story: it is a lie, it was a lie, it's a lie that's continually repeated and until we get an apology for it I will continue making sure people know it's a lie," Campbell said.

But, speaking on BBC radio earlier Thursday, Sambrook snapped back at Campbell for "seriously misrepresenting" BBC journalism.

"He said we had accused him and the prime minister of lying. That's not true. We haven't," Sambrook said.

"He said we accused the prime minister of misleading the (House of) Commons. We have never said any such thing. He said we were trying to suggest the prime minister had led the country into war on a false basis. We've never suggested that.

"He said the BBC had an anti-war agenda. That's untrue, we have no agenda. Finally he said we've not apologised. Well, that is true -- because we have nothing to apologise for."

Sambrook spoke on the Today program, the early-morning soap box of Britain's political class, whose defence correspondent Andrew Gilligan had orignally reported the allegation about the September dossier.

It was made by an unidentified individual close to the intelligence community who, Sambrook said, was "a senior, credible and reliable source."

According to the BBC, a one-sentence claim in the 50-page dossier -- that Iraq could deploy chemical and biological weapons within just 45 minutes -- was inserted under political pressure from Downing Street.

Many assumed that that pressure came straight from Campbell, a former tabloid political reporter with no shortage of enemies among politicians and journalists who resent the power he wields behind the scenes.

The British Broadcasting Corporation -- a vast web of radio stations, television channels, magazines and Internet sites, largely financed by a tax on television sets -- is fiercely protective of its editorial independence.

Parliament's foreign affairs committee is looking into the decisions that led to Britain's participation in the Iraq war. On Friday it will hear from Foreign Secretary Jack Straw for the second time this week, but behind closed doors.

Blair has ordered a separate inquiry by parliament's intelligence and security committee. Though it usually meets in camera, he has promised that its findings will be published.

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