The Democratic Party's front-runner Mr John Kerry has criticised the US President, Mr George W Bush over the apparent change in his rationale for waging war on Saddam Hussein's regime.
John Kerry
With no weapons found in Iraq, the administration had previously justified the war by arguing Saddam was worth toppling because of his appalling human rights record.
In today's interview on NBC's "Meet the Press", Mr Bush said Saddam Hussein had the capacity to develop unconventional arms if not the actual weapons.
"Now the president is giving us a new reason for sending people to war, and the problem is not just that he is changing his story now, it is that it appears he was telling the American people stories in 2002," Kerry said in Richmond, Virginia.
He called on Bush to allow a "legitimate and immediate investigation into the extraordinary failure" of US intelligence or whether the Bush administration hyped the threat for political purposes.
Last Friday Bush appointed a bipartisan commission to investigate flaws in intelligence used to justify the war based on former chief weapons hunter David Kay's fruitless search.
Bush said he gave the commission until March 2005 to report back because he did not want its work to be hurried and that voters will have ample time to assess "whether or not I made the right decision" in invading Iraq.
"It's important that this investigation take its time," he said.
Bush said CIA Director George Tenet's job was not in jeopardy but he blamed the intelligence he received for his pre-war convictions that Iraq was a danger.
"I expected to find the weapons ... I based my decision on the best intelligence possible, intelligence that had been gathered over the years, intelligence that not only our analysts thought was valid but analysts from other countries thought were valid," he said.
On "Fox News Sunday," Sen. John Edwards of North Carolina said the commission should fully investigate but he hoped it could finish before the election.
"It does bother me" that the commission is not slated to complete work until March 2005," he said. But, "The commission needs to conduct its study in a serious way. It shouldn't be politically motivated or politically driven. We need to get to the bottom of this."