The attack, involving small arms and mortar or rocket fire, started around midnight local time (1930 GMT Friday), Master Sergeant Bob Barko of Nato's International Security Assistance Force (Isaf) told AFP.

Another Isaf spokesman said the assault was over but details including the number of attackers and whether they managed to penetrate the British base -- a massive logistics hub spread over several square kilometres (miles) of desert -- were not immediately clear.

Barko said some troops had also been wounded in the attack but could not give precise numbers or nationalities.

A defence official in Washington said the two dead were US Marines, speaking on condition of anonymity.

A separate Isaf statement sent to AFP said that buildings and aircraft at the base had been damaged, without elaborating.

Prince Harry has been deployed at the base as a military helicopter pilot.

There was no immediate claim of responsibility after the attack.

Barko said that Isaf was assessing the extent of the damage to the camp in restive Helmand province, one of the toughest battlefields in the 10-year war, but the prince was not thought to have been affected.

"The information we have is that he was not in any danger," he said.