Iraq's former deputy prime minister, Tariq Aziz, told American interrogators that Saddam Hussein was alive in early April, but the truth of his statement was uncertain, a US official said on Monday.

Key former Iraqi officials in US custody, including Aziz and some scientists, were sticking to 'the party line' that Iraq had no biological, chemical and nuclear weapons programmes because they had all been destroyed, the official said.

US air strikes targeted Saddam and his sons, Uday and Qusay, in the Baghdad area on April 7 and March 20 Iraqi time.

Aziz, who surrendered to US forces in Baghdad last week, did not say that Saddam had survived the strike on April 7, but that the Iraqi leader was alive after the first one, the official said.

"Is he telling the truth? Don't know," he said.

"There is lots of evidence on all sides of every question."

Examination of the rubble at the two sites where Saddam was targeted has not yet uncovered any evidence to conclusively determine whether he survived, another US official said.

"We still have people sifting through the debris and trying to find evidence either way."

It was the ousted leader's 66th birthday on Monday.

In Iraq, a top US military commander said on Monday his forces were following up leads to try and find Saddam and his sons. Major General Buford Blount, commander of the 3rd Infantry Division, said there had been reports of sightings of Saddam's sons.

Blount said of Aziz: "He is being held in Baghdad. He is being questioned right now and the indications right now are that he is cooperating."

Asked what would happen to Aziz, Blount said: "I'm not sure what the disposition will be with him and others we are holding. The disposition will be determined in the future. For now they're going to be held for a while."

(Additional reporting by Rosalind Russell in Baghdad)