U.S. combat troops left the last of Iraq's cities on Tuesday, returning the country to Iraqi control in a move applauded by many Iraqis even though some fear it will leave them more vulnerable to attacks. By midnight on Tuesday, all U.S. combat units must have withdrawn from Iraq's urban centres and redeployed to rural bases, according to a bilateral security pact that also requires all U.S. troops to leave Iraq by the end of 2011. The last U.S. combat troops left central Baghdad on Monday, pulling back to two large bases near the capital's airport, and withdrawals from other cities were underway. Some troops tasked with training and advising Iraqi forces will stay behind. The pullout was marked with a bloody reminder of the six years of war unleashed by the 2003 U.S. invasion. Four U.S. soldiers from the Multi-National Division-Baghdad died of combat-related injuries on Monday, the U.S. military said, but gave no further details.