Afghanista - Afghanistan's President Hamid Karzai accused NATO on Thursday of killing a number of children in an airstrike, a case which could stoke tensions between the government and its western backers over a mounting civilian death doll.

The NATO-led coalition in the country did not immediately confirm the deaths, but said it was investigating an incident in the Najrab district of eastern Kapisa province.

Civilian deaths have been one of the biggest sources of friction in relations between the Afghan government and NATO ahead of a withdrawal of foreign combat troops in 2014.

"President Hamid Karzai strongly condemned an airstrike by foreign troops which resulted in the killing of a number of children," a statement from his office said.

Karzai had sent an advisor, Mohammad Zahir Safi, to the area to investigate the incident, the statement added.

Mehrabuddin Safi, the governor of Kapisa, said a coalition air strike late on Wednesday killed eight children in Giawa village. Other Afghan officials had earlier said the strike followed a night raid on suspected insurgents.