The details of the deaths of a US serviceman, a civilian contractor and three Afghan soldiers looked increasingly murky on Sunday after early reports suggested the incident was the result of an insider attack.

The shootout, which took place in the eastern Wardak province on Saturday, was initially blamed on Afghan soldiers. But NATO's Lieutenant General Adrian Bradshaw later told reporters that the incident could "possibly have involved insurgent fire."

"The incident occurred while an ISAF unit was manning a temporary checkpoint in an area near an Afghan National Army unit," Bradshaw said.

|"According to ISAF and ANA reporting, after a short conversation took place between ANA and ISAF personnel, firing occurred which resulted in the fatal wounding of an ISAF soldier and the death of his civilian colleague."

Bradshaw said the three ANA personnel died in an ensuing exchange of fire, but did not confirm whether they were killed by NATO troops.

Both NATO and the Afghan Defense Ministry have confirmed that a joint investigation into the incident is underway.

Increasing insider attacks

At least 51 coalition troops are believed to have died at the hands of their Afghan allies this year alone. That figure accounts for roughly 15 percent of all NATO deaths and is up from 35 deaths throughout 2011.Spiraling "green-on-blue" attacks have raised questions over the long-term prospects for Afghan security.

German magazine Der Spiegel published details of a report conducted by Germany's intelligence agency, the BND, on Sunday which suggested that insider attacks may be set to increase further.

Analysis published in the report entitled 'Afghanistan until 2014 - a forecast,' suggested that up to 35,000 foreign soldiers will need to remain in Afghanistan following the planned withdrawal of western combat troops in 2014. They will be required to train Afghan soldiers and combat terrorism.

With nearly 4,800 soldiers stationed in Afghanistan, Germany contributes the third largest force under NATO's International Security Assistance Force. A further 68,000 US troops and 9,500 British troops are based in the country.

On Sunday the US government announced that the number of American troops lost in the 11 year conflict had exceeded 2,000.

ccp/slk (AFP, Reuters)