From Fox News:

NATO spokesman Maj. Jason Waggoner says the attack happened Monday morning in southern Afghanistan. He says a man in an Afghan army  uniform killed two service members and the gunman was shot dead. He declined to  provide further details.

A Western official in southern Afghanistan confirmed that the incident happened at a base in Lashkar Gah, Helmand province, but declined to give further details. The official spoke on condition of anonymity because the information had not been officially released.

Other news from Afghanistan:

https://twitter.com/#!/TelegraphNews/status/184058618293923840

https://twitter.com/#!/Reuters/status/184008500979044353

https://twitter.com/#!/Michael_Yon/status/183973481334063104

https://twitter.com/#!/businessinsider/status/183740222381633536

https://twitter.com/#!/ArmyTimes/status/183914994704982016