Afghan authorities are investigating the deaths of at least 17 civilians during a clash between NATO forces and militants in southern Afghanistan, an official said Friday.

Villagers and a senior police official claimed Thursday that a NATO airstrike killed the civilians, including women and children, in Nad Ali district of the Helmand province.

The NATO-led force in Afghanistan confirmed that it carried out an airstrike in the area on Thursday — but not that it resulted in any civilian casualties.

NATO spokesman Capt. Mark Windsor said Friday the force was seeking more information and declined further comment.

Daud Ahmadi, spokesman for Helmand's governor, said Friday that authorities were investigating whether the airstrike or "insurgent action" caused the collapse of the house in which the civilians died.

Angry villagers brought more than a dozen corpses — including the badly mangled bodies of women and children — to the governor's house in the town of Lashkar Gah on Thursday, said Haji Adnan Khan, a tribal leader who had seen the bodies.

Nad Ali, about 6 miles from Lashkar Gah, has been a scene of heavy fighting between insurgents and Afghan and foreign troops. Militants control much of the area around the village.

The issue of civilian casualties at the hands of foreign troops has caused friction between Afghan President Hamid Karzai and his U.S. and other Western backers.

Karzai has for years warned the U.S. and NATO that it must stop killing civilians in its bombing runs or risk undermining his government and the international mission.

In the most prominent recent incident, the Afghan government said that 90 civilians were killed during a U.S. raid in western Herat province in August.

A U.S. military investigation found that 33 civilians died, and concluded that their troops acted in line with their rules of engagement.

Western commanders point out that militants put civilians at risk by operating from residential areas. Innocents also bear the brunt of insurgent bombings and suicide attacks.

Insurgency-related violence has killed more than 4,800 people — mostly militants — this year, according to an Associated Press count of figures from Western and Afghan officials.

In eastern Kunar province, meanwhile, a clash between Afghan forces and militants in Narang district late Thursday killed 18 insurgents, said Gen. Abdul Jalal Jalal, the provincial police chief.

Jalal said the insurgents had attacked an Afghan security checkpoint, sparking the clash.

It was impossible to independently verify Jalal's claim. Afghan officials are known to exaggerate their battlefield successes.