KABUL: An American soldier shot and killed an Afghan guard at a base in the country's north, apparently because the American thought the guard was about to attack him, Afghan police said on Sunday.

There have been a growing number of attacks by Afghan soldiers against international forces in Afghanistan in recent years, some the result of arguments and others by insurgent infiltrators. Last month, an Afghan soldier shot and killed four unarmed French troops last month at a base in eastern Afghanistan.

Friday's shooting in Sari Pul province in northern Afghanistan resulted from an unfortunate misunderstanding, said Sayed Jahangir, the deputy police chief for the province.

Afghans guard the outside perimeter of the base and Americans guard inside. Jahangir said that the Afghan guard _ a man named Abdul Rahim _ wanted to go into the base and started arguing with the American at the door. Rahim did not raise his weapon, but the American thought he was about to do so and fired, Jahangir said.

''Our initial reports show that the American thought he was acting in self defense,'' Jahangir said. Rahim was a private guard, not an Afghan soldier or policeman, Jahangir said.

US forces were ''aware of an incident in northern Afghanistan'' and were investigating, said US military spokesman Lt. Col. Jimmie Cummings. He declined to provide further details.