The head of BBC News has accused Downing Street press chief Alastair Campbell of waging a "personal vendetta" against the journalist behind the Iraq weapons row.
Campbell accused the BBC of lies
In a nine-page letter to Mr Campbell, Richard Sambrook firmly rejected claims that the BBC lied about the government's first dossier outlining the threat posed by Saddam Hussein.
He refused to give the apology demanded by Mr Campbell over defence correspondent Andrew Gilligan's report that a senior intelligence official told him the dossier was "sexed up".
Mr Sambrook's letter produced a swift response from Mr Campbell, who accused the corporation of "weaselly words" and "sophistry".
He said: "It confirms our central charge they (the BBC) do not have a shred of evidence to
justify their lie, broadcast many times on many outlets, that we deliberately
exaggerated and abused British intelligence and so misled Parliament and the
Speaking on Channel 4 News, Mr Campbell denied any personal agenda against Mr Gilligan - a man he said he had never met.
Mr Sambrook's letter escalated the war of words between the government and the BBC.
In it, he gave a point-by-point rebuttal of the spin doctor's attack against the BBC - which was made on Wednesday.
He wrote: "You will see that I do not accept the validity of your attacks on our journalism and on Andrew Gilligan in particular.
"We have to believe that you are conducting a personal vendetta against a particular journalist whose reports on a number of occasions have caused you discomfort."
Mr Sambrook said the source behind the claim was credible and it would have been wrong to suppress the story because there was only one source for it.
He said the BBC would have preferred the source to go public, but in such situations that was rarely possible.
Other newspapers had also reported intelligence sources being unhappy with government treatment of their information, Mr Sambrook added.
The government has branded as a "lie" the claim in the BBC report that extra prominence was given in the dossier at Downing Street's request to a claim that Iraq could launch weapons of mass destruction in 45 minutes.
Foreign Secretary Jack Straw on Friday again denied that claim, when answering questions by the Commons foreign affairs select committee on Friday.
He acknowledged the 45 minutes intelligence was not in the original draft of the dossier.
But he insisted that this was because the information did not come to light until September.
His words appeared to contradict Downing Street press chief Alastair Campbell's evidence that the 45 minutes claim was in the "very first draft" of the dossier.
The dossier was one of two issued by the government on Iraq - the second was the so-called "dodgy dossier" released earlier this year which plagiarised an academic work.
Gilligan stands by his story
During heated public exchanges on Friday, committee chairman Donald Anderson demanded the Commons foreign affairs committee be allowed to question the head of the Joint Intelligence Committee (JIC).
But Mr Straw accused Mr Anderson of trying to involve the government in a "turf war" with another Commons committee investigating the weapons row.