Prime Minister Tony Blair faced questioning by a top-level US panel on Iraq on Tuesday, as Britain and the United States grapple for a way forward in the violence-wracked country.
The British leader's testimony via videophone to the Iraq Study Group comes a day after he called for a change of strategy and pressed Iran to support Western efforts to quell the relentless bloodshed.
The US panel, led by former US Secretary of State James Baker, on Monday heard from US President George W. Bush, who defied growing calls for the West to engage with Syria and Iran.
Bush's and Blair's foes will no doubt be on the lookout for differences in opinion between the two men on how to turn around the campaign in Iraq, mired in increasing violence more than three years after the 2003 US-led invasion.
But Bush appeared in fighting form in his testimony, insisting that Iran must halt its nuclear program, while Syria must get its hands off Lebanon and stop shielding extremists before any talks can begin.
The United States accuses Syria and Iran of fomenting instability in Iraq and allowing insurgents to cross their borders.
"It's very important for the world to unite with one common voice to say to the Iranians that, if you choose to continue forward, you'll be isolated," Bush said in Washington. "There has to be a consequence for their intransigence."
Meanwhile Blair, Bush's main ally in the controversial 2003 US-led invasion of Iraq, set out his latest thinking in a keynote speech Monday evening in London.
In particular he said the three-year-old conflict -- in which US and British troops appear increasingly mired -- needs to be seen as part of a "whole Middle East" strategy.
"Just as the situation is evolving, so our strategy has to evolve to meet it," he said.
In the wide-ranging address, he said a major part of the answer to the Iraq problem "lies not in Iraq itself but outside it, in the whole of the region where the same forces are at work."
"Just as it is, in significant part, forces outside Iraq that are trying to create mayhem inside Iraq, so we have to have a strategy that pins them back, not only in Iraq but outside of it too .... This is what I call a 'whole Middle East' strategy," he said.
Blair also pressed Iran to help by cutting its aid to insurgents in Iraq, offering Tehran a "strategic choice" of forging a "new partnership" with the West or refusing its support and facing increasing isolation.
Pressure for a change of course in Iraq has been fuelled by the Republicans' defeat in US mid-term elections, which led to the departure of defence secretary Donald Rumsfeld and leaves Bush more vulnerable in a Congress.
Both Bush and Blair are fighting to counter criticism that they are lame ducks: Blair because he is set to stand down next year, and Bush because the Republican faces the last two years of his presidency fighting a Democrat-led Congress.
In that context, some observers question whether they can ultimately do anything to stem the rising tide of violence.
"They are in serious trouble in Iraq, they have to recognise it," said Rosemary Hollis, director of research on the Middle East at Chatham House, the London think-tank.
"They, Blair, Bush, seem to be trying convince themselves that their policies have not failed."
Blair was due to address the Washington panel by videolink from 1400 GMT on Tuesday, his office said, adding that aides would brief journalists afterwards on what he had told the US officials.