US soldiers killed in Afghanistan Helmand attack
Three US soldiers have been killed and one injured by a gunman wearing uniform in Helmand province, Nato has said.
Afghan officials told the BBC that the three were special forces members shot in the Sangin area late on Thursday.
The exact circumstances are unclear. Nato says it is the latest in a series of "green-on-blue" attacks, where men wearing Afghan army uniforms turn their guns on coalition troops.
But local officials say the three were killed by an elder they were meeting.
The elder said he wanted to join the police but in reality was a Taliban infiltrator, the officials told the BBC's Bilal Sarwary in Kabul.
Green on blue
A Nato spokeswoman told the Reuters news agency that it was too early to say whether it was a "rogue shooting or due to insurgent infiltration".
"All we know is that they were killed by an Afghan in a uniform of some sort," the spokeswoman said.
Throughout 2012 there has been a dramatic jump in "green-on-blue" killings, amounting to an average of one a week.
On Tuesday a US Nato soldier was killed by two gunmen wearing Afghan army uniform in eastern Afghanistan.
The attacks have led to a serious erosion of trust between Nato and Afghan forces.
In a separate incident on Friday, a roadside bomb killed at least six civilians - including women and children - in the Musa Qala district of Helmand province, local police chief Farid Ahmad Farhang told the BBC.
Also on Friday, the US government identified four Americans who died on Wednesday in an attack by two men wearing suicide vests in eastern Afghanistan.
Air Force Maj Walter Gray from the state of Georgia, Army Major Thomas Kennedy from New York, and Command Sgt Maj Kevin Griffin of Wyoming were named by the Department of Defense.
Secretary of State Hillary Clinton said the fourth victim was Ragaei Abdelfattah of the US Agency for International Development.
Her statement said three coalition service members and an Afghan civilian were also killed, and a state department diplomat was hurt.
Mrs Clinton condemned the attack, which the Taliban said they had carried out.