Nato troops are hoping to train Afghan forces so they can take over responsibility for security in 2014 [GALLO/GETTY] 

Six Nato troops have been killed by a man disguised as an Afghan policeman in during a training session in eastern Afghanistan.

The attack, which took place on Monday in Nangarhar province, is the latest in a series of similar attacks targeting foreign troops in Afghanistan.

"An individual in an Afghan border police uniform turned his weapon against  International Security Assistance Forces (Isaf) during a training mission today, killing six servicemembers in eastern Afghanistan," Isaf said in a statement released on Monday.

Isaf did not reveal the nationality of the dead troops, but the attack took place in a part of Afghanistan where US forces are locked in a deadly ongoing struggle against Taliban fighters.

The incident was the worst casualty toll  suffered by Isaf since eight troops were killed in five separate incidents on October 14.

The deaths bring the number of coalition troops killed in Afghanistan to 668, according to a tally kept by the AFP news agency, making it the deadliest years since the US-led invasion toppled the Taliban government in 2001.

The US military is bankrolling a training programme for Afghan forces so that they will be able to take responsibility for security in their country by 2014.

But the training programme has been infiltrated by fighters from the Taliban and other opposition groups who have carried out a series of shootings on international troops.

Monday's attack follows the deaths of two Nato troops on a military base in Sangin, a town in the volatile southern province of Helmand, earlier this month.

In July, two US contractors were killed by an Afghan soldier on a base in northern Afghanistan, and a week later three British Gurkha soldiers were killed by another rogue soldier.

On Sunday, the International Crisis Group (ICG), a think-tank, issued a  damning review of the war and said Afghan security forces "have proven a poor match for the Taliban".

The ICG said the police were "corrupt, brutal and predatory", the army was being manipulated by powerful tribal leaders, and that both forces suffered from a lack  of training and low retention among the ranks.

Source: Agencies