WASHINGTON -- President Barack Obama announced Friday that he’s accelerating the U.S. military withdrawal from Afghanistan, with the 66,000 American forces moving this spring into a largely training and advisory role and Afghan troops taking the lead throughout the country in fighting the Taliban-led insurgency.

Obama, addressing a news conference with Afghan President Hamid Karzai after several hours of talks, said the stepped-up pace of the pullout – further details of which are to be revealed in coming weeks – was possible because Afghan forces “continue to grow stronger” through the U.S.-led training and equipping program.

American troops will continue fighting alongside Afghan units when needed, but “their primary mission will be training, advising and assisting Afghan troops,” Obama said. “It will be a historic moment and another step toward full Afghan sovereignty.”

As of the end of September, according to a Pentagon report, Afghan security forces were in the lead in 85 percent of military operations. The transition of U.S. forces to a training and advisory role originally was to have taken place in early summer.

Obama’s upbeat assessment contrasts with the much darker situation on the ground more than 11 years after the U.S.-led invasion. Taliban and other insurgent groups remain potent despite the recently ended 33,000-strong surge of American troops, Afghan forces are unable to operate without American air and logistics support, and Karzai’s government is hamstrung by intrigue, corruption and incompetence.

Moreover, the Taliban and other insurgents remain secure in sanctuaries in the border regions of neighboring Pakistan and they persist in rejecting peace talks with Karzai until all foreign forces withdraw from Afghanistan.

But Obama, for whom Afghanistan was once a war of necessity, appears intent on ending America’s longest war as soon as possible, driven by its growing unpopularity and pressures to rein in military spending.

He acknowledged that Afghanistan “is going to still be very dangerous. But what we’ve seen is, is that Afghan soldiers are stepping up at great risk to themselves.”

The accelerated U.S. withdrawal sets the stage for the complete pullout of the American-led NATO combat mission by the close of next year.

“What that translates into precisely in terms of how this drawdown of U.S. troops proceeds is something that isn’t yet fully determined,” Obama said.

He said he was receiving recommendations from U.S. commanders on the pace of the drawdown as well as on the size of a possible American force that would remain after 2014 to train Afghan troops and prevent al Qaida from trying to re-establish sanctuaries in Afghanistan in which to plot attacks on the U.S. and allies.

Obama and Karzai, who was ending his first state visit to Washington since 2010, spent much of their talks ironing out some differences and discussing the terms of a bilateral security agreement that would govern the status of any American force that remains in Afghanistan after 2014.

Karzai said he’d won Obama’s agreement to hand over to Afghan custody “soon after my return to Afghanistan” some 600 high-value insurgent detainees whom the U.S. had declined to surrender last year when it turned over control of detention centers to Afghan officials.