British Prime Minister Tony Blair has said he is seeking a new United Nations resolution to ensure the handover of power in Iraq on 30 June.
Blair and Annan both want a UN resolution on Iraq
After meeting UN Secretary General Kofi Annan in New York, Mr Blair said there was now a common purpose in the international community over Iraq.
He also denied being disappointed with the US endorsement of Israel's plan for withdrawal from Gaza.
The talks came ahead of Mr Blair's meeting with President George W Bush.
One year after the fall of Saddam Hussein, coalition troops are up against renewed uprisings across the country.
Critics claim the Americans' use of overwhelming firepower to put down such opposition is serving only to unite the people of Iraq against the occupying forces.
US Defence Secretary Donald Rumsfeld has announced that some 20,000 US troops now serving in Iraq are to have their tours of duty extended.
At a joint news conference in New York with Mr Annan, Mr Blair confirmed that circumstances would require a new UN resolution ahead of the June handover.
He also confirmed that talks were continuing and that he and President Bush were waiting for the UN special envoy in Iraq, Lakhdar Brahimi, to come back with proposals which he has been discussing with the parties and stakeholders on the ground.
"We have to make sure we give Iraqis the opportunity they seek," he said.
Mr Annan said that divisions in the international community caused by the Iraq war were "beginning to heal", adding that he was hoping for the full co-operation of member states over a new resolution.
Turning to the US decision to back Israeli Prime Minister Ariel Sharon's unilateral plan for withdrawal from the Gaza Strip and some parts of the West Bank, Mr Blair denied that the roadmap for peace had been sidelined.
"If it is the case that the Israelis are withdrawing from Gaza, then that is quite a big change and let's use that and work upon it," he said.
Mr Blair arrived in the US on the day Arab television aired an audiotape said to be from Osama Bin Laden in which he offers Europe a truce if it "stops attacking Muslims".
BBC Washington correspondent Justin Webb says this could be the last time that Mr Blair and Mr Bush meet at the White House, as it is unlikely that the prime minister would visit during the upcoming presidential election campaign.
The meeting is being billed by officials as a routine get-together but our correspondent says it feels like more than that, partly because the situation in Iraq is so difficult and partly because of real differences on the way forward, in Iraq and in the Middle East more generally.
But he adds that there will be no public falling out, despite disagreements on the wisdom of the tough military tactics being employed by the Americans in Iraq and on the Middle East roadmap, which Mr Bush seems to regard as a low priority.