A member of the NATO-led force in Afghanistan and a civilian contractor have been killed in the latest insider attack by a member of the Afghan security forces, the coalition said Sunday. Other reports said they were both Americans.

Three members of the Afghan National Army were also killed in the firefight on Saturday, while three other U.S. citizens and one Afghan were wounded, police spokesman Wali Mohammad told Reuters.

The attack, which took place in eastern Afghanistan, came after the United States said joint operations with Afghan forces were returning to normal.

The attack took place in the Sayed Abad district of the Wardak province, according to local police sources, who said a gun battle broke out between coalition soldiers and Afghans when an Afghan National Army member opened fire on American troops.

"Initial reports indicate that a misunderstanding happened between Afghan army soldiers and American soldiers," provincial government spokesman Shahidullah Shahid told the Associated Press. He said investigators had been sent to the site to try to figure out what happened.

An Afghan official, speaking anonymously because he was not authorized to release details, told the New York Times that a mortar shell had landed amid the American forces, killing a soldier and a civilian contractor and injuring several others. The Americans thought it came from the Afghan National Army checkpoint and attacked it, killing several of the soldiers there, he said.

The provincial police chief Abdul Qayoum Baqizoi said the fight broke out when an Afghan soldier among seven soldiers at the checkpoint opened fire on the Americans; in the ensuing gunbattle, three Afghan soldiers were killed, including the one who had first opened fire.

“We still don’t have a clear picture of what happened,” Mr. Baqizoi said. He quoted one of the surviving Afghan soldiers as saying, “I heard some noise and verbal argument and suddenly heard the shooting and then one of the coalition soldiers threw a hand grenade so I fled from the checkpost and hid myself behind our Humvee.”

Joint operations were halted two weeks ago after a surge of attacks on the NATO-led International Security Assistance Force by its Afghan allies. At least 52 ISAF service members have been killed this year in "green-on-blue" attacks.

It was too early to say what impact the latest incident would have on plans to restore joint operations with Afghan troops to normal, a spokesman for ISAF said.

If the U.S. deaths are confirmed by Department of Defense, Saturday's insider killing would take U.S. civilian and military deaths in Afghanistan to over 2,000.

To contact the editor, e-mail: