President Barack Obama called Monday for NATO countries to sign off on his exit strategy from Afghanistan that calls for an end to combat operations next year and the withdrawal of the U.S.-led international military force by the end of 2014.

Against a backdrop of demonstrations that saw violent clashes between protesters and police, NATO and world leaders opened the second day of their Chicago summit with a focus on the unpopular war and how to pay for shoring up Afghanistan's security forces.

Obama told the dozens of heads of state in attendance, including Afghan President Hamid Karzai, that NATO can agree on both the timetable for withdrawing foreign forces from Afghanistan and a long-term plan for the strategic alliance to support the central Asian country's security forces.

The goal is to "responsibly bring this war to an end" in the next 19 months, Obama said in welcoming remarks Monday. He cited a recent strategic partnership agreement he signed with Karzai as a step toward ensuring that "as Afghans stand up, they will not stand alone."