KANDAHAR  - Three American special forces soldiers were shot dead Friday by an Afghan police officer who had invited them for a meal while six Afghan civilians were killed and another was injured when their vehicle hit a roadside bomb planted by Taliban insurgents in southern Afghanistan’s Helmand province, Afghan officials said.

The US military in Afghanistan confirmed that three US soldiers had been killed by “an individual in an Afghan uniform” in Sangin district of southern Helmand province, but gave no further details.

The attack was the third so-called green-on-blue assault, in which Afghan forces turn their weapons against their NATO allies, in just four days. Two Afghan officials told AFP the soldiers were shot dead by an Afghan police officer who had invited them for a meal at his checkpost in the restive southern province. “Asadullah, the police checkpost commander, invited four foreign special forces soldiers to (Ramazan) Sehri at 2:30 am in Sangin district,” a senior security officer in the province said, requesting anonymity.

“He later opened fire on the special forces soldiers, killing three and wounding another, and he managed to run away.”

The Sangin district chief, Mohammad Sharif, earlier told AFP that four foreign soldiers had been killed by the checkpost commander after he invited them to a meal. Taliban insurgents claimed responsibility for the attack, saying seven US special forces soldiers had been killed.

 “Asadullah (the police checkpost commander) joined the mujahideen ranks after the killing,” Taliban spokesman Qari Yousuf Ahmadi told AFP by telephone.

On Tuesday, an American soldier was killed in the east when two men in Afghan army uniform opened fire, and on Thursday an Afghan soldier was killed after turning his weapon on Nato troops, also in the east.

The latest deaths take the green-on-blue toll this year to around 33, in some 23 such incidents, according to an AFP tally.

Meanwhile, six Afghan civilians were killed and another was injured when their vehicle hit a roadside bomb planted by Taliban insurgents in southern Afghanistan’s Helmand province Friday, authorities said.

“Women and children were among the victims,” Helmand police spokesman Farid Ahmad Farhang told AFP, adding that they had been travelling in the Musa Qala district of the restive province.

Roadside bombs are a favourite weapon of Taliban Islamists fighting government forces and their NATO backers, but often miss their targets and kill civilians.

The latest deaths come two days after a report by the United Nations said 1,145 civilians had been killed and 1,954 wounded in the war in the first six months of this year.

The UN blamed 80 percent of the deaths on insurgents, saying more than half were caused by roadside bombs.