KABUL, Afghanistan — _ As NATO leaders prepared for a two-day summit in Chicago to plot their armed forces’ exit from Afghanistan in less than two years, a suicide bomber on Saturday detonated his explosive vest at a police checkpoint in eastern Khost province, killing 10 civilians, including two children, and three Afghan policemen.

The blast, which occurred at Ali Sher district on the border with Pakistan, also wounded five policemen and a child, said a spokesman for Khost governor’s office, Baryalai Rawan.

“The policemen were eating lunch when the explosion took place,” Rawan said. “The target of the attack was the police checkpoint, but civilians suffered most of the casualties.”

The Taliban in a statement on its website claimed responsibility for the attack, saying that it was carried out by a “holy warrior” named Abdul Haq from Khost province. The statement claimed that 12 soldiers had been killed and nine wounded.

In eastern Kunar province, two U.S. soldiers were reportedly killed on Friday when insurgents fired rockets at their base. The International Security Assistance Force (ISAF), the formal name of the U.S.-led coalition in Afghanistan, confirmed two ISAF members had been killed, but released no further details. In a statement, the Taliban claimed that its members had launched a major assault on a base belonging to “invading soldiers,” killing nine “foreign soldiers” and severely wounding eight others. The Taliban frequently exaggerate the number of casualties they inflict on ISAF and Afghan government forces.

Two women and a child were also killed at Kunar on Friday when a mortar round fired by insurgents hit a civilian house.

Afghan President Hamid Karzai is in Chicago for a NATO summit meeting beginning Sunday. The summit will discuss how NATO and the international community will support Afghanistan’s fledgling security forces beyond 2014, when the U.S.-led coalition is due to withdraw its combat troops.

Safi and Stephenson are McClatchy special correspondents.