The US military in Afghanistan says it has killed 11 Afghan civilians by mistake in an air attack.
A US Harrier jet dropped a 1,000 pound bomb
The deaths occurred when "a bomb dropped by coalition aircraft landed on a house... near the Pakistan border," a statement issued the US air base at Bagram said.
The statement said US planes had been responding to an attack by unnamed enemy forces on the outskirts of the town of Shkin.
US-led forces have launched a number of operations in recent weeks against members of the former Taleban regime and remnants of Osama bin Laden's al-Qaeda network.
The eleven dead civilians comprised seven men and four women, the statement said.
Another civilian was wounded.
"The tragic incident occurred when enemy forces attacked an Afghan military post checkpoint that was providing security near the Shkin firebase just before midnight last night," the statement said.
Two Harrier AV-8 jets then targeted two groups of enemy fighters.
One of the jets dropped a 1,000 pound laser-guided bomb.
"The bomb missed its intended target and landed on the house. The circumstances of the bombing are being investigated," the US statement said.
"Coalition forces never intentionally target civilian locations."
According to the statement, four Afghan Government soldiers were wounded in the enemy attack.
Earlier this week, the US said its troops had come under attack near Shkin, which is in the province of Paktika.
Correspondents say there has been growing resentment in southern Afghanistan as civilians have been caught up in a number of US-led security operations.
The issue of civilian casualties has caused controversy since the US launched its successful campaign to dislodge the former Taleban regime from control of Afghanistan.
US forces have launched several operations recently
In February local people in the province of Helmand said 17 people were killed when the US bombed a suspected Taleban base.
The US denied there had been fatalities.
Last July the New York Times published a report by an American aid group that said US air strikes had killed more than 800 civilians.
The aid group, Global Exchange, said the Pentagon relied on inaccurate or misleading information and preferred air strikes to ground operations that might put US forces at risk.
But a spokesman for President Hamid Karzai told the BBC civilian casualties were below 500.
In the most serious incident, the Afghan Government said 48 civilians - mostly women and children - were killed and 117 injured when a US AC-130 plane opened fire on a wedding party.
A US investigation concluded that the air crew were justified in attacking because they had come under fire.