The United States military says it is investigating the deaths of two American service members after a man wearing an Afghan National Police uniform used his weapon against them.
Military officials said Thursday's incident occurred in Uruzgan province. It is not clear if the attacker was a member of the Afghan National Security Forces.
The incident bears the hallmark of a so-called "insider attack," in which Afghan security forces or insurgents disguised in Afghan or coalition uniforms open fire on NATO personnel. Such attacks have escalated this year, killing more than 50 coalition troops.
Separately, British officials are investigating an incident from Wednesday, in which two British service members were killed in an "exchange of gunfire" in Helmand province.
Local Afghan officials tell the French news agency the incident was the result of "friendly fire," but British authorities have not confirmed that.
Elsewhere, Afghan officials say security forces killed a senior Taliban commander and 24 of his fighters in northern Afghanistan.
Officials in the governor's office of Faryab province said they sent reinforcements after insurgents attacked a village market. Five police officers died in the gunbattle.
Authorities say the Taliban commander, Yaar Mohammad, was the insurgent group's "shadow governor" of the region, enforcing the militants' own rule of law outside the central government.
The Taliban have traditionally been active in southern and eastern Afghanistan, but in recent years have spread their insurgency to the country's remote north.