A NATO airstrike killed eight children in Afghanistan's Kapisa province, President Hamid Karzai said Thursday.

The president "strongly condemned the aerial bombing by foreign troops that killed a number of children in Nejrab district" northeast of Kabul on Wednesday, said a statement from his office.

"Based on information by (the) provincial governor, as a result of an air strike conducted on February 8 in Geyawa village in Nejrab district of Kapisa province, eight children were killed," the statement said.

Karzai had assigned a delegation "to launch an all-out probe into the NATO bombing", it added.

A NATO spokesman said he could "confirm there has been a situation. A joint assessment team went there to identify the situation".

The Afghan president, who has a strained relationship with his Western allies, has regularly condemned NATO for civilian deaths in the decade-long war against Taliban insurgents fighting to overthrow him.

A record number civilians were killed in Afghanistan in 2011 -- the fifth straight year the death toll has risen, the United Nations reported last week.

A total of 3,021 civilians died -- mostly at the hands of insurgents -- up eight percent from 2,790 in 2010, the UN mission in Afghanistan (UNAMA) said in its annual report.

Taliban-led insurgents caused 77 percent of the deaths last year, up 14 percent from 2010, while pro-government forces were responsible for killing 410 civilians -- 14 percent of the total, the report said.

Most deaths attributed to NATO forces were a result of attacks from the air, but there was an overall decline of four percent in the number of civilians killed by pro-government forces, the report said.