The prime minister has pledged that America and Britain will not take over the long-term running of Iraq.

Speaking in the Commons, Tony Blair confirmed that there would be an interim period when military forces on the ground took control of the country.

But he pledged to seek UN endorsement for the transitional arrangements before the running of the country is finally handed over to the Iraqi people.

Amid reports of differences between Britain and the US over post-war arrangements, Blair indicated there were some differences between the allies but said they were the subject of on-going discussions.

He told MPs that the body set up to govern Iraq after Saddam Hussein should be "UN endorsed".

With the issue dominating the weekly session of prime minister's questions, Blair appeared confident of international agreement despite differences between governments.

"I don't doubt there are differences in the UN but I believe those differences are not insurmountable," he said.

Blair said there would be a period when the allied armed forces took "de facto" control of the country but stressed that this would be a short-term arrangement.

"As soon as possible Iraq should not be run either by the coalition or the UN but by the Iraqis," he told the Commons.

Conservative leader Iain Duncan Smith sought clarification on whether "it should be for the United Nations to run Iraq or endorse a different administration".

And Charles Kennedy asked whether the British call for a post-war UN conference on Iraq was supported by America.

Blair said that both sides of the Atlantic recognised that "any interim authority has to be UN endorsed".

The prime minister pointed to the example of Afghanistan and said that the allies and the UN would be able to work together.

But the Liberal Democrat leader said the government should be "more specific about what the thinking is".

"Do he and the president of the United States envisage that the post conflict situation will be UN-led or American-led?" Kennedy asked.

Blair repeated that Iraq should be run by the Iraqis, and the "process of transition" should be organised by both the coalition forces and the UN.

"The basic principle is that any transitional arrangements and the Iraqi interim authority has got to be UN endorsed and the rest of it, frankly, is a matter of working in partnership with the UN, which if we behave sensibly we should be able to do very easily," he said.

"Iraq in the end should not be run by the Americans, should not be run by the British, should not be run by any outside force or power. It should be run for the first time in decades by the Iraqi people."