Geoff Hoon has told MPs that Britain would be "failing in its duty" to an ally if it did not agree to an American request to send troops to a US controlled sector south of Baghdad.

Advance elements of a British battle group of 900 soldiers could be heading to the area within days, if the Cabinet approves the Bush administration's request for the reinforcements on Thursday.

Ministers are facing angry opposition to the move with some MPs suggesting that it was aimed at helping President Bush's re-election.

Dennis Skinner, the Labour left-winger, said that a deployment before the election would be "handing out an oxygen cylinder to President Bush".

But Hoon defended the proposed move. "Were we to refuse the request it would go to the heart of our relationship not only with the US but with other members of the alliance," he said.

Yesterday the US Marines who are expected to be replaced by the British troops repeatedly came under heavy attack from militants.

The Independent carries quotes on its front page from Labour MPs who backed the war but are rejecting this plan.