Al Jazeera's James Bays, reporting from Kabul, the capital, said that the deaths were caused by an air raid.

"There have been civilians that were killed in what Isaf is admitting is an air strike carried out by their aircraft. They say they are investigating the incident."

Uncertain casualties

Bays said that Nato had called in air support for operations to attack three locations in the area.

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He added that some locals have said that up to 32 people in total were killed, including two children.

"The number of fatalities is not clear but locals at the scene are telling us that ... people were killed as they were taking away the bodies from an earlier attack.

"But there has been no word from the Taliban ... about this incident."

Separately, Afghan officials said that at least seven police officers were killed in northern Afghanistan after a suicide car bomber struck a joint Afghan-Nato convoy.

Six other officers were injured along with five Afghan civilians in the attack, which occurred while the convoy was on patrol in the Imam Sahib district of Kunduz province.

"The bomber was in a car and struck the convoy. Six police and one pro-government guard were killed," Abdul Rahman, a senior provincial police officer, told the Reuters news agency.

Major Michael Johnson, a spokesman for Nato forces, said there were no Nato troops killed in the bombing.

Violence peak

Violence in Afghanistan is at its worst since US-led and Afghan armed groups overthrew the Taliban in 2001.

The Taliban, who are largely active in the south and east, have stepped up their attacks in recent months in some areas of the north, which had previously been considered relatively safe.

Despite a record number of foreign forces in Afghanistan - standing at some 140,000, backed by thousands of Afghan forces - the Taliban has managed to spread its campaign out of its traditional powerbases and into the north of the
country.

June was the bloodiest month for foreign forces in the nine-year-war, with more than 100 troops killed.

Hundreds of Afghan civilians have also been killed this year as they become increasingly caught up in the crossfire.

Kunduz has taken the brunt of the Taliban attacks in the north and the fighters are increasingly using it as a base to launch attacks elsewhere in the region.