British forces handed over military control of the Basra area to US commanders Thursday to clear the way for America's main battlefield ally to exit Iraq after more than six years of war. The US flag rose over a British base outside Basra, the last main outpost for about 4,000 British forces in southern Iraq who will almost all withdraw by the end of May. At the height of combat operations after the March 2003 invasion, Britain had 46,000 troops in Iraq. Washington still has about 130,000 troops in the country and has shifted units south ahead of the British pullout. American troops operate alongside Iraqi soldiers who have taken over many front-line roles in the strategic Basra area, the hub of British military operations for years. “Today marks the closing chapter of the combat mission in Iraq,” British Prime Minister Gordon Brown said in London after meeting with Iraqi Prime Minister Nuri Al-Maliki. The Iraq war has been extremely unpopular in Britain, and the issue shadowed the final years of Tony Blair's premiership. Since the 2003 US-led invasion, 179 British service personnel have been killed in Iraq. The British military dedicated a memorial wall to those killed Thursday, part of the preparations for withdrawal. “They will always be remembered for the service they have given. Our country owes them a huge debt of gratitude,” Brown said. British commanders have been gradually handing over responsibility of the oil-rich Basra region to the US military since March and have been withdrawing troops from the country in phases. Nearly all of its troops are expected to be withdrawn by May 31, British military officials have said.