KHOST, Afghanistan (Reuters) - The U.S. military has conceded that a raid this week by troops under its command in Afghanistan killed a group of civilians who were defending their home, not militants as it had earlier reported.

A villager looks at a bloodied door of a house after a military raid in a village in Gurbuz district of Khost province April 9, 2009. REUTERS/Kamal Sadat

The killing of civilians by foreign forces is the biggest source of tension between the Afghan government and its Western backers. While NATO has tightened its procedures, the latest incident shows the problem is far from solved.

Investigations showed that during an operation by U.S. and Afghan forces in the southeastern province of Khost late on Wednesday, a local family near the target location had opened fire on the troops, the military said in a statement late on Thursday.

“The combined forces returned fire, killing two males, two females and wounding two females. There are reports of an infant also killed,” the statement said.

“Coalition and Afghan forces do not believe that this family was involved with militant activities and that they were defending their home against an unknown threat,” it added.

A Reuters witness at the village after the raid saw the body of a seven-day-old boy who died during the raid.

International aid group Care said in a statement that one of the victims was a female teacher working in a school it supports. It said the four others killed were members of her family, including two children. One was a student in her class.

PROTEST AND REGRETS

The Khost Provincial Council has closed its offices in protest until foreign troops commit to ending all unilateral raids not coordinated with Afghan forces, and raids that cause civilian casualties, council head Najibullah Gurbuz told Reuters.

“We will keep our office closed until foreign forces promise us not to carry out such raids again, which cause the death of civilians, and those who have carried out this attack and have killed these civilians should be brought to justice.”

The commander of international forces in Afghanistan last year issued a tactical directive to all foreign troops allowing only Afghan troops to take the lead in raids on homes unless a clear danger is identified.

The United States said it regretted the deaths.

“Words alone cannot begin to express our regret and sympathy and we will ensure the surviving family members are properly cared for,” the military statement quoted U.S. Brigadier General Michael Ryan as saying.

Some 2,100 civilians were killed in Afghanistan last year, a third of them by Afghan and international troops, the United Nations says.

Violence in Afghanistan has reached its highest level since the 2001 U.S.-led invasion, despite a growing number of foreign troops, and has spread from the south and east to the outskirts of the capital, Kabul.

Afghan and U.S.-led coalition forces killed 36 Taliban fighters in southern Helmand province on Friday, a spokesman for the provincial governor said. Insurgents killed six policemen in an attack on a post in Nawa district, further south.