An air strike appears to have killed 12 members of an Afghan family, most of them children, the United Nations said, citing preliminary findings, as US and Afghan forces ramp up aerial bombardments against militants.

The latest incident brings to at least 21 -- including 14 children -- the number of civilians killed in air strikes in recent days, according to the UN Assistance Mission in Afghanistan (UNAMA).

Sunday night's air strike destroyed a house in Wardak province near Kabul, killing 12 members of a family, UNAMA said in a statement late Tuesday.

The victims included 10 children aged six to 15 and two women.

The findings support earlier comments from provincial council member Ahmad Jahfari, who told AFP that 12 members of a family had been killed in an air strike targeting Taliban fighters.

A villager called Abdullah told AFP that two of his sisters died in the attack that he said claimed the lives of more than 12 civilians.

"Three other houses were also destroyed," Abdullah said.

“They wanted to bomb a Taliban prison about 100 metres (330 feet) from our house."