The US is the only country capable of leading the military operation in Iraq, Jack Straw has suggested.

The comments came as the foreign secretary held talks with UN secretary general Kofi Annan in New York.

The visit follows Tuesday's bomb blast at the UN's headquarters in Baghdad.

Tuesday's attack left over 20 dead and 100 injured and has raised the spectre of a fresh wave of terror in the region.

Amongst those killed was United Nations special representative in Iraq, Sergio Vieira de Mello.

During talks with the secretary general, Straw explored options aimed at engaging the UN in the political and social reconstruction of Iraq.

The foreign secretary played down suggestions that the US was attempting to use Tuesday's terror attack to bounce UN members into committing troops to a peacekeeping operation on the ground.

"What we've been discussing above all is what happens next in Iraq and... ways in which the international community could come together to strengthen the mandate of the United Nations and the role which the international community is taking," he said following the talks.

Despite the united front, both Straw and Annan suggested that significant obstacles to a second UN resolution still existed.

Earlier this week, the foreign secretary signalled that Britain has an "open-mind" on calls for a new UN resolution covering the security situation on the ground in Iraq.

He added that Britain and the US believe the UN must play a "vital role" in Iraq.

"What what we want to see is a collaborative process so we have a resolution that represents a broad consensus," he said.

But Straw warned that it would not be practical to suggest that the UN could take the lead military role on the ground.

"If you think about the numbers of troops the United States has compared to any other country, it means that if you want there to be an effective military operation then the command has to be through the United States," he said.

Straw hopes he will be able to overcome UN hostility to Washington's call for Europe "to do more" to assist in the international peacekeeping effort.

Washington threatened to open new splits in the UN on Thursday when Colin Powell signalled that America believed other UN countries should give more support to an international peace keeping force.

Anti-war nations such as France, Russia and India said the White House was attempting to exploit Tuesday's Baghdad bombing to garner troop contributions.

They have warned that any peace-keeping force must have the full authority of the UN and have refused to operate under US command.

The foreign secretary also repeated his condolences for those killed in Tuesday's atrocity.

"I said to the secretary general, and to his colleagues in the meeting, that in the two and a quarter years in which I have been very closely associated with the United Nations as Britain's foreign minister, it has come home to me more and more that the United Nations is not just an international organisation, it is also a community and a family," said Straw.

The long-planned trip comes on the eve of the UK's one month presidency of the security council.