Gunman in Afghan army uniform kills 2 NATO troops A gunman wearing an Afghan army uniform killed two NATO troops in southern Afghanistan on Monday. The incident appeared to be the latest attack by rogue Afghan security forces on Western troops. "The individual who opened fire was killed when coalition forces returned fire," NATO's International Security Assistance force said in a statement. It did not identify the two NATO soldiers or give their nationality. The incident 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. Staff Sgt. Bales' wife to TODAY: 'He would not do that' So-called 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 Korans 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. 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, NBC News' Cheryll Simpson and msnbc.com staff contributed to this report.