Updated 3:05 AM ET
(CBS/AP) KABUL, Afghanistan - At least one Afghan police officer turned his gun on coalition troops in a remote base in southern Afghanistan before dawn Sunday, killing four U.S. soldiers, according to a provincial source.
A high ranking source in Zabul province tells CBS News that the incident happened inside a joint U.S. and Afghan base in Mizan district of Zabul province last night when an Afghan policeman opened fire on coalition security forces, killing four and injuring two before he was shot dead. The source added that 16 other policemen who were on the base have either been arrested by NATO forces or may have fled.
It was the latest in a string of insider attacks by Afghan forces against their international counterparts that are threatening the military partnership between Kabul and NATO, a partnership that is key to the handover of security responsibilities to Afghan forces as international troops draw down. The day before, a gunman in the uniform of a government-backed militia force shot dead two British soldiers in the south.
"The attack took place in the vicinity of an outpost in southern Afghanistan. It is my understanding that it was a checkpoint," Jamie Graybeal, a spokesman for the international military in Afghanistan said. International forces often work with Afghan police to man checkpoints as part of the effort to train and mentor the Afghan forces so that they can eventually operate on their own. The goal is to turn over all security responsibility for the country to the Afghans by the end of 2014, though numbers of NATO forces have already been reduced in some areas.
The coalition said in a statement that they are investigating what happened.
There were also international troops wounded, Graybeal said. He said that early reports showed two were hurt and that they were receiving treatment. He did not say how serious the injuries were.
So far this year, 51 international service members have died at the hands of Afghan soldiers or policemen or insurgents wearing their uniforms. At least 12 such attacks came in August alone, leaving 15 dead.