Afghan army soldier kills NATO service member

KANDAHAR, Afghanistan (Reuters) - An Afghan army soldier killed at least one foreign soldier in southern Helmand province on Saturday, a senior police source said, underlining persistent insecurity as NATO prepares to hand over to Afghan troops.

The latest in a series of "rogue" shootings by members of the country's security forces occurred barely 25 km (15 miles) from the city of Lashkar Gah, where this week security control will be handed to Afghan forces.

It is one of seven places chosen for the first phase of a years-long transfer due to be completed only by the end of 2014.

"The shooting happened during a joint security patrol ... he ran away after," said the senior police detective, who asked not to be named as he was not authorized to speak to the media.

The NATO-led International Security Assistance Force said it was investigating an incident in southern Afghanistan.

"An individual wearing an Afghan National Army uniform turned his weapon against International Security Assistance Force service members in southern Afghanistan today, killing one service member," ISAF said in a statement.

Taliban spokesman Qari Mohammad Yousuf said an ANA (Afghan National Army) soldier surrendered to the Taliban after killing five foreign soldiers outside Lashkar Gah this morning.

"He wasn't one of us, he asked for protection and we agreed," Yousuf told Reuters by phone from an undisclosed location. The hardline Islamists often exaggerate death tolls and battlefield exploits.

U.S. and NATO forces are ramping up efforts to train the Afghan army and police for the gradual transition.

Highlighting the difficulty of that task, however, have been a series of incidents over the past 18 months where Afghan police and soldiers, or insurgents who have infiltrated security forces, have turned their weapons on their mentors.

There was another such incident in Helmand in May, when two U.S. troops were killed at a police compound.

(Reporting by Ismail Sameem, writing by Emma Graham-Harrison, editing by Elizabeth Piper)