U.S. chopper crashes in Afghanistan; 6 dead

Updated at 9:28 a.m. Eastern

KANDAHAR, Afghanistan - A NATO helicopter has crashed in southern Afghanistan, killing six members of the international military force, the U.S.-led coalition said Friday.

Sources in Afghanistan and Washington tell CBS News it was a U.S. Marine CH-53 helicopter that crashed, and a U.S. military official tells the Associated Press that all those killed were Marines, but the coalition has not officially disclosed the nationalities of the victims. Details of such incidents are generally kept private until the families of the dead are notified.

CBS News is still seeking independent confirmation on the nationalities of the crash victims.

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The cause is still being investigated, but a coalition statement said there was no enemy activity in the area at the time of Thursday's crash, which brought the number of international forces killed in Afghanistan this month to 24.

CBS News correspondent Mandy Clark reports that some military sources are pointing to a likely mechanical failure, but they say it's too early to determine exactly what brought the helicopter down in the Taliban-dominated area.

The Taliban claimed responsibility for bringing the helicopter down in a statement to CBS News, but Clark says the militant group often exaggerates claims of military success. NATO has denied any Taliban involvement.

It was the deadliest crash in Afghanistan since August, when 30 American troops died after a Chinook helicopter was apparently shot down in Wardak province in the center of the country.

The helicopter crash occurred on the same day that a rogue Afghan soldier opened fire on French troops in the country on a training mission, killing four and leading French President Nicolas Sarkozy to immediately halt all training operations in Afghanistan. He also said he may consider pulling all French troops out of the country sooner than planned.

Meanwhile, a suicide car bomber killed at least seven civilians Thursday outside a crowded gate at Kandahar Air Field, a sprawling base for U.S. and NATO operations in the south. The Taliban insurgents claimed responsibility, saying they were targeting a NATO convoy.

It was the second suicide bombing in as many days in southern Afghanistan, officials said. The coalition said no NATO troops were killed Thursday. It does not disclose information about wounded troops.

The Taliban have been stepping up attacks in southern Afghanistan, the birthplace of the insurgency, with a wave of bombings and the assassinations of three local Afghan officials this week. The violence comes even as the U.S. is moving ahead with plans for negotiating with the Taliban to try to end the 10-year-old war in Afghanistan.