KABUL — A suspected militant on a motorbike threw a hand grenade at the gates of a school in north Afghanistan on Sunday, injuring 17 children, the interior ministry said in a statement.

The incident took place in Maimana, the main city of Faryab province, the ministry said, adding that the children had been taken to hospital, with two in a serious condition.

"Seventeen school students were wounded when a terrorist gunman riding a motorbike threw a hand grenade at the main gate," said the statement, which condemned the attack.

"Police have arrested the gunman who committed this action."

An annual UN report in March revealed that the deaths of Afghan civilians in the war had increased 15 percent to a record high last year, and that insurgents were responsible for three-quarters of the killings.

Foreign forces are due to begin handing over seven areas of the country to Afghan control from next month, after nearly ten years fighting the Taliban-led insurgency, with all combat troops due to leave by the end of 2014.