The left-wing British daily said the two men voiced concerns about intelligence on Iraqi weapons during a private meeting in New York.

The encounter came shortly before a key UN Security Council meeting on February 5, when Powell presented what he claimed was clear evidence that Iraq was concealing banned weapons, the Guardian said.

Its story was based on information from a unnamed diplomatic source, who the paper said had read a transcript of the conversation between Straw and Powell.

The transcript recorded Straw voicing concern that assertions being made by British Prime Minister Tony Blair and US President George W. Bush about Saddam Hussein's arsenals could not be proved.

The document quoted Powell as allegedly saying he was "apprehensive" about intelligence assessments containing circumstantial evidence, and telling Straw he hoped the facts, when they came out, would not "explode in their faces".

The Guardian, which opposed the US-led war against Iraq, said that the transcript appeared to have been leaked by diplomats who were supportive of the use of force against Baghdad at the time, but now feel they were lied to about its justification.

But the Foreign Office dismissed the Guardian report as "simply untrue" and insisted that "no such meeting took place" between Powell and Straw.

Meanwhile, US Secretary of State Colin Powell was under persistent pressure from the Pentagon and White House to include questionable intelligence in his report on Iraq's weapons of mass destruction he delivered at the United Nations last February, a US weekly reported Friday.