At least two people, thought to be U.S. marines, have been killed in a militant attack on a major International Security Assistance Force (ISAF) base in southern Afghanistan, British media reported on Saturday.

The base’s perimeter was breached as small arms fire was opened; buildings, an aircraft hangar and a few military jets were seriously damaged in the attack, launched in the facility’s U.S. area, Sky News reported.

The attack might still be ongoing, a spokesman at ISAF's Joint Command said.

The British TV broadcaster cited Afghan officials as saying that the base has often been subject to indirect fire. They added, however, that this time the damage is more severe.

It was unclear whether the attack had been caused by an anti-Muslim YouTube movie that has sparked protests in the Middle East, Africa and Asia.

British Prince Harry is currently based at Camp Bastion on his second tour of duty in Afghanistan.