Updated at 3:15 a.m. Eastern.
Six Afghan national police officers were beheaded Tuesday by militants who stormed their checkpoint in the country's north, according to NATO, which earlier reported the deaths of two American civilians and two Afghan troops at another installation in the north.
The military coalition said in a statement issued Wednesday the militants attacked a number of government buildings, including a police checkpoint, in Baghlan province's Dahanah-ye Ghori district. The insurgents overran the checkpoint and killed the officers inside by cutting off their heads.
Local officials could not be immediately reached for comment.
Violence and casualties have surged in recent months in Afghanistan. June was the deadliest month for U.S. and international forces with the deaths of 103 service members, including 60 Americans.
Earlier Wednesday, NATO said two American civilians and two Afghan soldiers were killed in a shooting on a base outside Mazar-e-Sharif.
An Afghan soldier who trained others at the base started shooting during a weapons exercise Tuesday, the international military coalition said in a statement.
The shooter was one of those killed, and it was not immediately clear if he targeted someone or if bullets had gone astray. It also was not clear how many people fired weapons.
NATO and Afghan forces are jointly investigating, Defense Ministry spokesman Gen. Mohammad Zahir Azimi said. There were no immediate details on the U.S. civilians, but contractors commonly work as trainers at such bases.
The Washington Post reported Tuesday that CIA director Leon Panetta and Defense chief Robert Gates were concerned over the extent to which America's war efforts relied on private contractors.
Intentional shootings by Afghans against coalition partners have occurred previously but still are rare.
Earlier this month, an Afghan soldierwith gunfire and a rocket-propelled grenade in the dead of night.
The soldier fled after that attack, leaving his motive unclear. But the Taliban claimed he was a militant sympathizer taken in by insurgents after the assault.
In November, an Afghan policeman killed five British soldiers at a checkpoint in Helmand.
The attacks come as the international coalition is ramping up training of Afghan soldiers and policemen so they can ultimately take responsibility for securing and defending the nation.
The speed with which Afghan security forces are growing - the allies set an interim goal of expanding the Afghan army from 85,000 in 2009 to 134,000 troops by October 2011 - has raised concerns about infiltration by the Taliban and the professionalism of the forces.
President Hamid Karzaihis government's commitment to assume total responsibility for security in Afghanistan by 2014 - three years after President Obama intends to begin withdrawing U.S. troops.