Ramadi, Iraq ? The U.S. Marines marked the end of nearly seven years in Iraq on Saturday by handing the Army their command of Anbar province, once one of the war’s fiercest battlefields but now a centerpiece of U.S.-Iraqi cooperation.

The changing of the guard — overseen by military brass and some of Anbar’s influential Sunni sheiks — signals the start of an accelerated drawdown of American troops as the U.S. increasingly shifts its focus to the war in Afghanistan.

American commanders are trumpeting security gains in places such as the western Anbar province as a sign that their partnership with Iraqi security forces is working, and that the local troops can keep the country safe.

But fears are growing about a possible resurgence in sectarian tensions — fed by the Shiite-dominated government’s plans to blacklist more than 500 parliamentary candidates over suspected links to Saddam Hussein’s regime.

In Baghdad, U.S. Vice President Joe Biden met with Iraq’s leaders Saturday to try to alleviate the pressures. While he kept expectations of a breakthrough low — telling reporters after a meeting with President Jalal Talabani it was up to the Iraqis, not him, to resolve the issue — his visit alone underscored Washington’s concern.

The White House worries the bans could raise questions over the fairness of the March 7 parliamentary election, which is seen as an important step in the American pullout timetable and a way to break political stalemates over key issues such as dividing Iraq’s oil revenue.

“I am confident that Iraq’s leaders are seized with this problem and are working to find a just solution,” Biden said during his visit.

The Marines formally handed over U.S. responsibility for Sunni-dominated Anbar, Iraq’s largest province, to the Army during a ceremony at a base in Ramadi, the scene of some of the war’s most intense fighting. Overall control of the province shifted from the U.S. military to Iraq in September 2008, but the U.S. continues to provide support for Iraqi forces.

As many as 25,000 Marines were in Iraq at the peak of the fighting, mostly in Anbar province. Fewer than 3,000 remain. All but a handful will ship out in a matter of weeks.

If all goes as planned, the last remaining Marines will be followed out by tens of thousands of soldiers in the coming months. President Barack Obama has ordered all but 50,000 troops out of the country by Aug. 31, with most to depart after the parliamentary election in March.

The remaining troops will leave by the end of 2011 under a U.S.-Iraqi security pact.

Later, after his meeting with the Iraqi president, Biden announced the U.S. will appeal a court decision dismissing manslaughter charges against five Blackwater Worldwide guards involved in a deadly 2007 Baghdad shooting.

Biden’s announcement shows just how diplomatically sensitive the incident remains nearly three years later. A lawyer for one guard, noting that word of the intended appeal came in Iraq, accused the Obama administration of political expediency and said the U.S. was pursuing an innocent man, rather than justice.