Abdul Khaleq / AP
An Afghan policeman checks a man entering the police station near the gate of a joint civilian-military base where two British soldiers part of the NATO forces were killed south of Kabul in Afghanistan.
Updated at 12:26 p.m. ET: Three NATO troops were killed in Afghanistan on Monday in two separate attacks apparently carried out by members of local security forces.
A gunman wearing an Afghan army uniform killed two NATO troops in southern Afghanistan, while another was shot in eastern Afghanistan by an alleged member of the Afghan Local Police.
The deaths appeared to be the latest in a string of so-called "green on blue" attacks in which Afghan security forces have turned on their international colleagues or mentors.
The incident in which two died took place in Lashkar Gah in the southern Helmand province, an Afghan security source told Reuters. It will be investigated by a joint Afghan-NATO team.
"The individual who opened fire was killed when coalition forces returned fire," NATO's International Security Assistance Force (ISAF) said in a statement about that incident. It did not identify the two NATO soldiers or give their nationality.
The Lashkar Gah base is dominated by British forces and a NATO official told The Associated Press the two victims were British soldiers. The official spoke on condition of anonymity because the information had not yet been formally announced.
Britain's Ministry of Defense said it was aware of the Lashkar Gah incident, but refused to release any more details or confirm whether the soldiers were British.
In a later statement about the shooting in eastern Afghanistan, ISAF said: :According to operational reports, the ISAF service member was shot by an alleged member of the Afghan Local Police as the security force approached an ALP checkpoint. The circumstances behind the incident are currently under investigation by Afghan and coalition forces."
There were no further details immediately available.
Insider attacks have mounted in recent months as tension between Afghanistan and its foreign backers rises over a series of incidents including the burning of Qurans at a NATO base and the killing of 17 villagers in southern Kandahar for which a U.S. soldier has been charged.
Before Monday's attack, 13 members of the NATO-led force had been killed this year in what appeared to be attacks by members of Afghan forces, the commander of U.S. and NATO forces, General John Allen, told a U.S. Senate committee last week.
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About 70 members of the NATO force have been killed in 42 insider attacks from May 2007 to January this year.
The shootings raise new concern about the reliability of Afghan forces and their ability to take over security responsibilities by the end of 2014, when most Western combat forces leave.
Reuters, The Associated Press, NBC News' Cheryll Simpson and msnbc.com staff contributed to this report.
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