A U.S. warplane mistakenly killed 11 civilians, most of them women, when a 1,000-pound laser-guided bomb missed its intended target today and landed on a house in eastern Afghanistan, the U.S. military said.

For the first time since the U.S-led coalition opened the war in Afghanistan in October 2001, the military immediately claimed responsibility for killing civilians, calling the deaths a "tragic accident" and promising to investigate the error. In the past, it has acknowledged such incidents only after investigations.

Afghan government ministers predicted that the errant bomb, which fell as Taliban fighters have been regrouping and launching attacks along the Pakistani border, would spawn new acts of terrorism aimed at destabilizing the U.S.-backed government of President Hamid Karzai.

"The fallout is going to be with us for a while," Interior Minister Ali Ahmad Jalali said. "This is a war, however, a war on terrorism, and these things happen. The American response was very rapid because their mistake was very clear. They hit a family compound."

The killings occurred about 130 miles south of Kabul in Shkin, in eastern Afghanistan near its unstable border with Pakistan. The area is a favorite passageway for Taliban fighters and other rebel forces based in Pakistan. U.S. and Afghan government forces maintain posts there and are frequent targets of attacks.

The 11 civilians killed, along with a wounded survivor of the bombing, were members of the same family, the governor of Paktika province said angrily this evening. They were killed early this morning, just after the local community had heard the first call to prayer of the day.

The chain of events began just before midnight on Tuesday, when a small band of men the U.S. military described as "enemy forces" attacked an Afghan military checkpoint that had been providing security for a U.S. base of operations in the region.

Afghan soldiers battled their attackers, then called for U.S. air support, U.S. military and Afghan officials said. Four Afghan soldiers were wounded in the initial fighting.

As the enemy forces fled and scattered, U.S. Marine Harrier jets attacked one group with cannons and attempted to bomb a second band of five to 10 rebel fighters, a U.S. military spokesman at Bagram air base said. "That bomb missed the intended target and landed on the house," a statement released by the U.S. military said. "The circumstances of the bombing are being investigated."

The Karzai administration said it would send its own team to investigate and try to defuse an increasingly tense situation in the region. "There is a lot of trouble in this area," Jalali said. "That's why our forces and the U.S. forces maintain a strong presence there. They are regularly being attacked."

The Afghan coordinator for Global Exchange, a human rights group that last year reported that U.S. bombs have killed more than 800 civilians in Afghanistan, lamented the muted response to today's deaths. "This time the military admitted their mistake right away, and nobody is even focusing on it," Nilufar Shuja said. "With the war in Iraq, 11 dead isn't even getting airplay in Afghanistan. It's kind of sad."