Hundreds of U.S.-led troops have launched an offensive against Al Qaeda and Taliban militants in an area of eastern Afghanistan where Usama bin Laden once hid, officials said Wednesday.

A bomb attack near the capital, meanwhile, killed three German police officers assigned to protect their country's embassy.

Ground troops and airstrikes are targeting "hundreds of foreign fighters" dug into positions in the Tora Bora region of eastern Nangarhar province, coalition spokeswoman Capt. Vanessa Bowman. She did not say when the operation began or how long it was expected to last.

The remote mountainous area bordering Pakistan was heavily bombarded in late 2001 by the U.S. troops hunting Usama bin Laden and his associates following the Sept. 11 attacks on Washington and New York. Bin Laden is believed to have escaped that assault.

There were no immediate reports of casualties among militants or U.S. and Afghan troops in the new operation.

The German police officers' two-vehicle convoy was traveling on an unpaved road about six miles southeast of Kabul when it was hit by an explosion that flipped and badly damaged one of the vehicles.

Interior Minister Wolfgang Schaeuble called the explosion an "underhanded attack."

The officers apparently were on their way to a training session, traveling in a "particularly well-protected vehicle," Schaeubel said.

He said Germany's Federal Crime Office was sending experts to Afghanistan to help investigate the explosion. The wounded officer, who did not suffer life-threatening injuries, was being treated by the German military at a Kabul base.

Amir Mohammad, a police officer, said he believed the device was a land mine but it was not clear if it had been recently planted.

Afghanistan has suffered nearly three decades of civil war and conflict, and is one of the most heavily mined countries in the world.

U.S. soldiers and French troops with anti-mine equipment arrived at the scene after the explosion. Afghan police kept reporters away from the site as forensic experts collected evidence.

Separately, U.S.-led coalition and Afghan troops clashed with militants in central Logar province on Tuesday, killing nine suspected militants, the Interior Ministry said. No police or coalition troops were wounded in the clash, it said.