BBC director general Greg Dyke has delivered a stinging rebuke to the US media over its "unquestioning" coverage of the war in Iraq and warned the government against allowing the UK media to become "Americanised".

Mr Dyke said he was "shocked" to hear US radio giant Clear Channel had organised pro-war rallies in the US and urged the UK government to ensure new media laws did not allow American media companies to undermine the impartiality of the British media.

"We were genuinely shocked when we discovered the largest radio group in the United States was using its airwaves to organise pro-war rallies," said Mr Dyke.

"We are even more shocked to discover the same group wants to become a big player in radio in the UK when it is deregulated later this year.

"The communications bill currently before parliament will, if it becomes law, allow US media companies to own whole chunks of the electronic media in this country for the first time.

"In the area of impartiality, as in many other areas, we must ensure we don't become Americanised."

The BBC chief expressed his concern that American media owners would apply the same pressure to their output in this country.

"You're surprised when you discover the biggest owner of American radio stations organised pro-war rallies - it's a long way from our idea of impartiality.

"They [American networks] must be clear that the rules are different here. What is now defined as impartiality in the US is different."

Mr Dyke singled out Fox News for particular criticism over its pro-Bush stance, which helped the Rupert Murdoch-owned broadcaster to oust CNN in the US to become the most popular news network.

"Commercial pressures may tempt others to follow the Fox News formula of gung-ho patriotism, but for the BBC this would be a terrible mistake.

"If, over time, we lost the trust of our audiences, there is no point in the BBC," he said in a speech delivered at Goldsmiths College in London today.

Mr Dyke revealed there had been a huge increase in demand for BBC news in the US since September 11, saying this reflected "concerns about the US broadcasting news media".

"Many US networks wrapped themselves in the American flag and swapped impartiality for patriotism. What's becoming clear is that those networks may have misjudged some of their audience.

"Far from wanting a narrow, pro-American agenda, there is a real appetite in the US for the BBC's balanced, objective approach."

Mr Dyke also mounted a rigorous defence of the BBC's coverage of the war in Iraq after ministers publicly accused the corporation of bias towards the Baghdad regime.

He refuted accusations that the BBC had been "soft" on Saddam Hussein, insisting the corporation's commitment to "independence and impartiality" was "absolute."

Mr Dyke added the BBC had made "subtle daily changes" to the way it covered the war so it could "believe in and defend the integrity of our reporting".

Citing the history of war reporting from Suez through Vietnam to Kosovo, Mr Dyke said British governments of every persuasion had sought to use the media to manage public opinion.

"In doing so they have often sought to influence the BBC and, on occasions, to apply pressure," he said.

Mr Dyke conceded the government had a right to pressurise the BBC, saying it would only become a problem if the BBC caved in to its demands.

But he dismissed accusations from Downing Street that BBC correspondents in Baghad were Hussein's stooges as "absurd," saying that although journalists such as Rageh Omaar had Iraqi minders who occasionally restricted their movements, "they did not interfere with what was being broadcast".

He did, however, admit the war had raised new dilemmas, one of these being the controversial practice of embedding journalists with troops.

"Embedded correspondents may have given us better pictures and immediate insight of the battles but how much physical risk for our journalists and crews is acceptable in return for great pictures and commentary?" he asked.

"How do we ensure their reports are placed in the proper context; how can we guard against 'embeds' being seen as 'in bed' with their hosts?

"On this latter point, I think there is a need here for a serious piece of academic research on the impact of embedded journalism."