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Former British Foreign Secretary Robin Cook said in diary excerpts published Sunday that he believes Prime Minister Tony Blair knew two weeks before the war that Iraq probably didn't possess usable weapons of mass destruction.

The claim by Cook -- who resigned from the government over the U.S.-led war -- renewed calls for an investigation into why Britain joined the invasion despite questions about the threat posed by Saddam Hussein.

"I think this vindicates those of us who have been calling for an independent judicial inquiry into the reasons why we went to war," said Alice Mahon, a lawmaker in Blair's ruling Labor Party and a leading opponent of military action in Iraq.

Blair's office shrugged off Cook's claims.

"The idea that the prime minister ever said that Saddam Hussein didn't have weapons of mass destruction is absurd," a spokesman said on condition of anonymity. "His views have been consistent throughout, both publicly and privately, as his cabinet colleagues know."

In excerpts from his diaries published in The Sunday Times newspaper, Cook said he was most concerned with a conversation he had with Blair on March 5, two weeks before Britain went to war. At the time, the government was still trying to get a fresh U.N. resolution to approve the conflict and Cook was still in government as leader of the House of Commons.

Cook said he told Blair that briefings he had received made it clear Saddam had no weapons of mass destruction "that could strike at strategic cities" and asked the prime minister if he was concerned that the Iraqi leader would use chemical munitions against British troops.

Cook said Blair's response was: "Yes, but all the effort he has had to put into concealment makes it difficult for him to assemble them quickly for use."

The former minister writes in his diary, to be published in book form as "Point of Departure," that he was deeply troubled by two elements of the exchange.

"The first was that the timetable to war was plainly not driven by the progress of the UN weapons inspections. Tony made no attempt to pretend that what (former chief UN weapons inspector) Hans Blix might report would make any difference to the countdown to invasion," he writes in a March 5 entry.

"The second troubling element to our conversation was that Tony did not try to argue me out of the view that Saddam did not have real weapons of mass destruction that were designed for strategic use against city populations and capable of being delivered with reliability over long distances."

Cook said he had also expressed that view to John Scarlett, chairman of the Joint Intelligence Committee, and that Scarlett had similarly failed to correct him.

Blair's government made the threat of Iraqi weapons the heart of its case for military action, and the prime minister has been on the defensive because coalition forces found no such weapons. The government has also faced criticism over its treatment of David Kelly, a government official and scientist caught up in a political storm over the Iraq war who committed suicide.

An inquiry into Kelly's death has touched on the reasons Blair joined the U.S.-led invasion of Iraq. But critics of the war said Cook's claims proved the need for a new inquiry looking specifically at the government's case for military action.

"If these allegations are true they are explosive," said Menzies Campbell, foreign affairs spokesman for the opposition Liberal Democrats.

"We need an inquiry headed by a judge to look into the question of whether we went to war on a flawed prospectus, either because of inadequate intelligence or the mishandling of intelligence once obtained.