NATO leaders have gathered amid tight security in Turkey for a summit set to be dominated by the future of Iraq.

Tony Blair is joining 26 world leaders including President Bush for the Istanbul talks.

Discussions will centre on Iraq, Afghanistan, the future of the alliance and plans to train and equip the Iraqi army.

Ahead of this week's handover of sovereignty to the people of Iraq, Britain's ambassador to Baghdad has warned of difficult months to come.

Speaking on Sunday David Richmond said problems would continue well beyond June 30.

"I think probably the security situation will continue to be difficult for several weeks and maybe several months to come but I think there are very good reasons to think that the situation will improve as we move into the autumn," he said.

"There will be more Iraqi security forces who have been trained, enabling the multinational force to move into the background, the end of occupation itself will make a huge psychological difference, and the imminence of elections as we move into the autumn will make a difference in convincing Iraqis that now they are going to take charge of their own destiny."

Asked what role British troops would play over coming weeks, Richmond added: "It's quite difficult to answer that question at this stage. That depends on the level of
violence.

"It's clear that the multinational forces will want to adopt a lower profile, to try to withdraw to bases, and if the security situation allows that that's what will happen."

But he denied that coalition forces did not have a legitimate role to play following the handover.

"They have a mandate under the security council resolution to help and assist Iraqi security forces in maintaining security and maintaining order," he said.

"I think what we will see over the coming months is that more and more Iraqis will be trained and equipped and able to take the lead in providing security and that process will allow multinational forces to move into the background."

Meanwhile US defence secretary Donald Rumsfeld has signalled that NATO chiefs are poised to give the alliance a greater role in Iraq - although America is unlikely to secure support for a full security and stabilisation force under alliance control.

"In the case of Iraq, we anticipate that at this summit, the heads of state will end up agreeing that NATO will in fact have a role in training and equipping the Iraqi security forces, which is a very good thing if that happens," he said.

His comments were welcomed by Liberal Democrat foreign affairs spokesman Menzies Campbell.

"It is not in anyone's interests that Iraq should become a failed state," said Campbell.

"If NATO training of armed forces assists progress towards democracy it is obviously desirable that the allies should do so.

"However the terms of any proposals should not involve NATO being drawn into the command structure."