British troops are prepared for peace duty after the war

The new leader of the Commons' remarks followed those of Welsh Secretary Peter Hain who said the UN should be in charge once the interim post-war administration hands over power.

But on the BBC's Politics Show, Mr Reid said: "What we want is a interim administration that is representative of the Iraqi people and endorsed and drawing its authority from the United Nations.

"What some people appear to think is that the United Nations runs every aspect of an administration.

"It should be backed by the authority and the endorsement of the United Nations but it does not mean to say that in Bosnia or Kosovo or Afghanistan, the United Nations run every aspect of that administration.

"I think that is, by and large, agreed with the Americans."

US PLANS FOR POST-WAR IRAQ Bush advisers split on UN role Post-war building blocks in place Security fears delay rebuilding US outlines post-war Iraq plans

Mr Blair is understood to want the UN to be involved not only in the early provision of aid and reconstruction, but also in the setting-up of a new government for Iraq.

Foreign Office minister Mike O'Brien conceded that there was a "fair degree of confusion" about what was planned for Iraq.

He told BBC Radio 4's World this Weekend programme that immediately after the war the coalition military would restore law and order in Iraq.

Then retired US general Jay Garner would be responsible for initial rebuilding from ensuring the provision of water and food through to helping businesses start up again.

That would last "a few short months" before the handover to an Iraqi administration that would continue to work closely with American advisers until elections could be held.

"The UN don't want to run Iraq - they don't run countries. They will be involved in the post-war humanitarian effort and the handover to the Iraqi interim authority," he said.

'Show restraint'

Meanwhile former culture secretary Mr Smith urged US forces to show similar "restraint and patience" in the battle for Baghdad as their British allies had shown in the days before they began the advance into Basra.

But appearing on the BBC's Breakfast with Frost programme, Defence Secretary Geoff Hoon insisted that coalition forces were going to "extraordinary lengths" to avoid civilian casualties.

Mr Smith is critical of the war in Iraq

"I think we have to see how things develop in Baghdad. Baghdad may prove to offer the same kind of problem as Basra has - that is, some resistance from the militia, but also a need to avoid significant civilian casualties," he said.

"I am sure the Americans will approach this in a cautious way."

He also said that although troops would remain to ensure security in a post-war Iraq they would not stay a day longer than necessary.

Mr Smith also insisted that the UN must have a key role in a post-Saddam administration in Iraq.

"It has to have the stamp of United Nations authority on it. I want to make sure this is a process that is led, that is determined that is authorised by the United Nations with many different nations contributing."