Mr Cheney said: "There has not been another attack on the United States. And that's not an accident."

But Democrat Senate Minority Leader Harry Reid countered: "Vice-President Cheney's influence over our nation's foreign policy has made America less safe."

White House spokesman Tony Snow insisted Mr Bush's TV address would not be "a political speech".

"It is a reflection of what 11 September has meant to the president, and to the country; the realities that it has brought to all of our attention and how we can move forward together to try to win the war on terror," Mr Snow said.

Mr Bush's ratings soared after 11 September, but have declined with the war in Iraq and growing doubts about the administration's handling of the "war on terror".

Even as the president laid the wreaths at Ground Zero, crowds of protesters calling for a US withdrawal from Iraq gathered nearby.

As the anniversary began, CNN broadcast what it said was a new video featuring al-Qaeda's Ayman al-Zawahri.

He refers to the recent Israeli bombardment of Lebanon and the capture of Israeli soldiers by Hezbollah.

He says: "You gave us every legitimacy and every opportunity to continue fighting you.

"You should worry about your presence in the Gulf and the second place you should worry about is Israel."