KABUL, Sept 12 (Reuters) - U.S.-led coalition airstrikes killed nearly a dozen Islamist Taliban fighters in the southern province of Zabul overnight, the U.S. military said, as the bloodiest period since the militants' 2001 ouster grinds on.

Afghan and U.S.-led coalition troops called in air support after detecting a group of more than 20 Taliban preparing to ambush them near a village in the Arghandab district of the province on Tuesday, it added.

"The Afghan National Army called in coalition close-air support to strike the insurgents before they could launch their attempted ambush," the U.S. military said in a statement.

"The coalition aircraft used a precision-guided munitions and machine-gun fire to eliminate the insurgent threat."

"Nearly a dozen Taliban fighters were killed during the brief engagement," it added, saying more than 245 Taliban had been killed in the southern provinces of Kandahar and Zabul since late August.

There were no independent accounts of how many people were killed or what happened. The Taliban were not immediately available for comment.

The fighting came after a suicide bomber rammed a U.S. security firm convoy in the southern province of Helmand on Tuesday, killing two local staff and wounding eight other people.

The U.S.-led military says coalition forces have killed hundreds of Taliban militants in a series of confrontations in recent weeks. The Taliban have admitted some losses, but say Afghan and foreign troops vastly exaggerate enemy death tolls.

More than 7,000 people have been killed during the past 19 months in Afghanistan.

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