PHILADELPHIA, Oct 25: Former president Bill Clinton entered the Democratic election campaign for John Kerry on Monday saying he had cut short his recuperation from heart surgery because of the close race.

Kerry also stepped up pressure on President George W. Bush over Iraq, demanding answers about reports that nearly 380 tons of explosives had disappeared in Iraq.

Democratic favourite Clinton was to join Kerry at a rally in Philadelphia on Monday, kicking off the final week of the battle for the White House.

Clinton's appearance comes just seven weeks after he underwent quadruple bypass heart surgery. Clinton is also to talk for Kerry in Florida and in the western United States this week.

He is still hugely popular with Democrats despite the sex scandal that tarnished his presidency. The party hopes he will inspire party faithful to turn out on November 2, when turnout could decide the result.

Clinton told ABC television he was throwing himself into the campaign "because it is close and because I think it is important and because the differences between the candidates and the courses they will pursue in the next four years are so profound."

The ex-president said the United States is split down the middle over the election.

"Each party has a base vote of about 45 percent. So the election will turn on what percentage of that 45 percent shows up, who has done a better job of registering, what percentage shows up."

He went on "I think this is one of the most difficult elections to call I have ever seen."

White House communications director Dan Bartlett said Clinton's return revealed Kerry's weakness.

"The fact that John Kerry's going to have to roll him off the surgery table and onto the campaign trail demonstrates a revealing aspect, that he's underperforming in key parts of his own constituency," Bartlett told Fox television.

The Kerry campaign meanwhile seized upon a report by the International Atomic Energy Agency that nearly 380 tons of explosives that could be used for conventional or nuclear missiles had disappeared from an unguarded military installation in Iraq.

The Iraqi authorities had informed the IAEA of the disappearance of the HMX and RDX explosive materiel on October 10, agency spokeswoman Melissa Fleming said.

"It can be used in a nuclear explosion device, for the explosion," she said, adding: "That's why it was under IAEA verification and monitoring" before the March 2003 US-led invasion of Iraq.

She added that the agency feared the powerful explosives may have "fallen into the wrong hands, terrorists."

"Today, the Bush administration must answer for what may be the most grave and catastrophic mistake in a tragic series of blunders in Iraq," senior Kerry advisor Joe Lockhart said in a statement dispatched before sunrise.-AFP