KABUL, AFGHANISTAN - NATO said Saturday it was investigating reports that an Afghan soldier had shot and killed foreign troops, while a NATO official said on condition of anonymity that two US Marines had died.
The alliance's media office said it was aware of "the incident in Helmand province," which was reported by Pakistan-based Afghan news agency Afghan Islamic Press (AIP).
A team from ISAF and the Afghan government "is investigating the incident" but could provide no further details, NATO's International Security Assistance Force (ISAF) told AFP in a brief statement.
A NATO official who spoke on condition of anonymity said two US Marines were killed in the "green-on-green" incident, late on Thursday night.
"They weren't shot in their beds, they must have been on guard duty," the official said.
"Rounds were fired within the FOB (forward operating base) and an Afghan soldier was found to be missing the next morning," he said.
The Afghan soldier had joined the FOB within the last "two or three weeks and not a lot was known about him," he said.
Helmand's deputy police chief Colonel Kamaludin Khan said earlier: "We know that an army soldier opened fire on ISAF forces but we don't know the details."
AIP is not generally regarded as reliable and often publishes Taliban propaganda.
In a report early Saturday, AIP quoted a Taliban spokesman saying an Afghan soldier had "shot and killed three foreign troops at a base in Sangin district of Helmand".
"The ANA soldier opened fire on foreign troops at base in Tamirano area close to the headquarters of Sangin last night, killing three foreign soldiers, Qari Muhammad Yousuf Ahmadi, spokesman of Taliban, told Afghan Islamic Press," the report said.
It quoted Ahmadi saying the "soldier fled the base and joined Taliban". Incidents in which Afghan soldiers or police officers turn on Western troops are rare, but raise questions about the multi-billion-dollar international effort to train and mentor Afghanistan's security forces.
In July a renegade Afghan soldier shot and killed three British army Gurkhas and wounded several others on a base in Helmand province.
That incident followed another in November last year, in which an Afghan policeman shot dead five British soldiers at a checkpoint, also in Helmand where most of Britain's troops are based.
The United States and NATO have more than 150,000 troops in Afghanistan fighting the insurgency, which is concnetrated in the southern provinces of Helmand and Kandahar.
More than 600 foreign soldiers have been killed in the Afghan war so far this year, compared with 521 in 2009.