Kabul, Afghanistan ? NATO extended its security mission Thursday to all of Afghanistan nearly five years after the West began its war to defeat the Taliban, taking command of 12,000 U.S. troops in the war-battered country’s east.

The handover diminishes the Pentagon’s role in Afghanistan and gives the Europe-based military alliance its biggest test yet.

The transfer of command “illustrates the enduring commitment of NATO and its international partners to the future of this great country,” said British Gen. David Richards. He was promoted to the military’s top rank hours before a handover ceremony at the NATO compound in Kabul attended by President Hamid Karzai and U.S. Lt. Gen. Karl Eikenberry.

The takeover caps an already historic expansion for the military alliance that was created as a Cold War bulwark against the Soviet Union. The mission in Afghanistan is the biggest ground combat operation in NATO history and gives Richards command of the largest number of U.S. troops fighting under a foreign commander since World War II.

The move comes during a rapid spread of the Taliban insurgency, with close to 100 suicide attacks this year, a nearly fivefold increase over 2005. Almost 200 civilians and soldiers have been killed. According to an Associated Press count based on Afghan, NATO and U.S. figures, more than 3,000 people have died in violence this year, mostly militants.

“NATO has never been tested like this, ever,” said Seth Jones, a RAND Corp. expert on Afghanistan. “They’ve got an extraordinarily difficult task ahead of them.”

With NATO handed the lead role, Washington has shed some responsibility for a stability project that appears to be headed in the wrong direction. U.S. voters readying for midterm elections have expressed fatigue with the Bush administration’s twin wars in Iraq and Afghanistan.

Increasing the international role in Afghanistan – which America has been unable to do in Iraq – could disarm critics who say President Bush mishandled the war. But few Muslim countries have joined the international effort, with fewer than 500 troops from Muslim nations.