Two American soldiers were shot and killed by one of their Afghan colleagues Monday morning, while 10 Afghan soldiers were killed in an "insider" attack on a checkpoint in Southern Afghanistan, according to military officials. Violence in the region, including a steady rise in 'green on blue' attacks, have continued to plague US and NATO forces there.

Details of the first incident involving the death of two American soldiers are uncertain but military personnel say the shooting may have been an accident. Officials say the Afghan soldier may have tripped amid chaos caused by an insurgent attack and accidentally discharged his weapon; however, there have been conflicting accounts of the incident.

"He didn't do this intentionally. But then the commander of the unit started shouting at him, 'What did you do? You killed two NATO soldiers!' And so he threw down his weapon and started to run," Noman Hatefi, a spokesman for the Afghan army corps in eastern Afghanistan reported. At that point US air support fired on the running Afghan soldier from above, killing him, Hatefi said.

In a separate episode in the southeast, 10 Afghan soldiers were killed at a checkpoint in Helmand Province. Officials said the soldiers were killed by insurgents posing as Afghan military.

"The Taliban attacked a post in Washir and killed 10 soldiers. Four other soldiers were wounded and five others have gone with the Taliban with their guns. It was an insider plot," said senior police official Colonel Mohammad Ismaiel Hotak.

The killing of American soldiers brought the number of coalition soldiers shot by Afghan police and military forces so far this year to 42, 12 of them this month alone.

There have been at least 33 insider attacks so far this year, killing 42 coalition members. Last year there were 21 attacks, killing 35; and in 2010 there were 11 attacks with 20 deaths.