Prime Minister Tony Blair and President George Bush have stressed their joint resolve to stick to the 30 June deadline for handing power to Iraqis.
Blair and Bush put on a united front
At a joint news conference, Mr Blair declared: "We will do what it takes to win this struggle.
"We will not back down in the face of attacks either on us
or on defenceless civilians," he said.
Like Mr Bush, he backed Israeli Prime Minister Ariel Sharon's controversial plans for Palestinian land.
But Iraq was the focus of the talks amid the continuing violence in the country.
Mr Blair has arrived back in the UK following the summit.
It follows disquiet about some of the US military's tactics.
Former Foreign Secretary Robin Cook urged Mr Blair to tell the president "bluntly" he was pursuing the wrong policies.
And Liberal Democrat leader Charles Kennedy said heavy-handed tactics by US troops risked driving young Muslims into the arms of radicals.
Conservative leader Michael Howard said he was disappointed there had been no mention of appointing a senior British official as the deputy head of the coalition.
Britain was "punching above its weight" militarily because of the strength of its armed forces, said Mr Howard.
"We are seen to be punching a bit below our weight in Iraq politically and diplomatically because we lack that powerful voice and because we do not have a sufficient say on day-to-day decisions on what is happening on the ground."
Whatever the words in private, Mr Blair showed public solidarity with Mr Bush in the White House rose garden.
"We mourn each loss of life," he said. "We salute them and their families for their
bravery and their sacrifice.
"Our promise to them in return is clear. It is to succeed. To get the job
done. To ensure their courage and sacrifice has not been in vain."
Mr Blair said the United Nations would play a "central role" in the transition of power in Iraq, and he hoped for a new Security Council resolution on the country.
Mr Bush declared: "The prime minister and I have made our choice. Iraq will be free. Iraq will
be independent. Iraq will be a peaceful nation and we will not waver in the face
of fear of intimidation."
The summit has coincided with indications from senior US officials that they are prepared to accept a plan prepared by UN special envoy Lakhdar Brahimi.
It proposes replacing the US-appointed Iraqi Governing Council with a caretaker government after the 30 June handover.
With those preparations continuing, the attention this week has switched back to the Middle East peace efforts.
Mr Sharon plans to withdraw from Palestinian land in the Gaza Strip, but retain Jewish settlements built in the West Bank in defiance of international law.
There had been speculation that Mr Bush's support for the plan this week would have irritated the prime minister.
But Mr Blair insisted the existing "roadmap" peace plan was not being abandoned, nor did the proposals prejudge any final settlement in the Middle East.
"What it does give us is at least the possibility of moving it forward," he said.
He urged the international community to "get involved" with the plan.
Mr Bush called the plan a good opportunity. "It gives the Palestinians a chance to create a reformed, just and free
Lib Dem leader Charles Kennedy said Mr Blair's endorsement of the Israeli plan risked fuelling Palestinian resentment.