The Taliban in Afghanistan have claimed responsibility for an attack on a base that killed two American marines, saying it was in retaliation for a film insulting the Prophet Mohammad.
The attackers managed to penetrate Camp Bastion in southern Helmand province and damage aircraft but a US military spokesman declined to say what type and how many.
He said initial estimates of insurgents killed ranged from 15 to 20.
According to the Reuters news agency, Camp Bastion came under mortar, rocket-propelled grenade and small arms fire early Saturday.
A US official said an initial report estimated five Americans were wounded but added that the extent of their injuries was unclear.
Violence against American targets has been spreading since the film triggered an attack on the US consulate in the Libyan city of Benghazi that killed the ambassador and three other Americans this week.
Prince Harry unharmed
Camp Bastion is a huge and heavily fortified base housing thousands of US, British and other troops. It is the base where Britain's Prince Harry is stationed but the third in line to the throne is reported to be unharmed.
Prince Harry, an Apache helicopter pilot, began a four month deployment in Afghanistan earlier this month.
Earlier this week, the Afghan Taliban said they were doing everything in their power to either kill or kidnap the prince in what they dubbed their "Harry Operations."
International Security Assistance Force spokesman Martyn Crighton said ISAF would investigate whether his presence on the base had motivated the attack.