KANDAHAR/SYDNEY - Taliban armed with guns and rockets stormed a heavily fortified airfield in Afghanistan where Prince Harry is deployed, killing two US Marines and attacking aircraft in a major security breach while two Nato soldiers were shot dead by a man believed to be member of local police in southern Afghanistan on Saturday.

The attack on Camp Bastion in southern Helmand province started at 10:15 pm (1745 GMT) on Friday and the base was cleared on Saturday morning, said US Army Major Adam Wojack. Prince Harry was never in danger, officials confirmed. Although the Taliban have vowed to kill the third in line to the British throne, one of its spokesmen told AFP that the assault "had nothing to do with the prince".

General Sayed Malook, the head of the Afghan army in the south, said a suicide bomber blew himself up, blasting a hole in the perimeter wall and allowing insurgents to storm inside with guns and rocket-propelled grenades.

"As soon as they entered the base, fighting started. Afghan forces were not involved, they only helped to extinguish the fire," Malook told AFP.

A fuel reservoir and an aircraft hangar were set alight during the attack and it took until dawn to extinguish the blaze, he said.

Wojack said it was not immediately clear how the attackers had penetrated the airfield, which is used by both American and British forces, but confirmed that aircraft had been damaged.

Eighteen insurgents were killed - including the suicide bomber - and another was captured and wounded, said Wojack. They were dressed in camouflage, he said, but declined to say whether it was Afghan army uniform.

A defence official in Washington said two US Marines were killed, and Nato's US-led Isaf said some personnel were wounded. A Taliban spokesman claimed the attack was waged to avenge a low-budget American YouTube film which has incited a furious wave of deadly anti-American violence in Yemen, Libya and Sudan, and protests in many other countries.

Isaf said it was assessing the extent of the damage to the camp, but the prince, who will spend four months at the base, was not affected.

"He was not in any danger," said Master Sergeant Bob Barko of Isaf. Two Nato soldiers were shot dead on Saturday by a man believed to be a member of Afghan police force in southern Afghanistan, the US-led military said.

"An individual believed to be an Afghan Local Police (ALP) member turned his weapon against (Nato's) Isaf service members in southern Afghanistan today, killing two," Isaf said.

The attacker was killed in return fire, the military said, refusing to disclose the nationality of the victims.

The police spokesman for southern province Helmand said the incident happened in the provincial capital Lashkar Gah on Saturday afternoon.

Meanwhile, police in Sydney fired pepper spray to contain protesters trying to enter the building housing the US consulate Saturday, as a wave of unrest against a film mocking Islam spread to Australia.

Bottles, shoes and other objects were hurled during the clashes with police which resulted in eight arrests, with six police officers injured as the unexpected protest brought parts of the city to a standstill.

"Police stopped the group attempting to enter the MLC centre that houses the American consulate," police superintendent Mark Walton told reporters of the clash, which left some protesters weeping from the impact of the spray.

On Saturday shoppers looked on in surprise as protesters shouted "Down, down USA" and waved banners such as "Behead all those who insult the Prophet (PBUH)" and "Obama, Obama, we love Osama".

"We are sick and tired of everyone mocking our beloved Prophet (PBUH)," protester Houda Dib told AFP, as the crowd of about 500 gathered outside the US consulate.

"They have no right to mock our Prophet (PBUH). We don't go around mocking anyone's religion."

Demonstrators were pushed back from the steps outside the consulate by police, who then used capsicum spray, provoking anger among some in the crowd, many of whom had brought their children with them.

Further clashes broke out with police before the crowd eventually dispersed.

Two police cars were also damaged in the protest which saw some 150 police deployed to the central business district.

Separately in Tunis, the Tunisian health ministry said Saturday that four people were killed and almost 50 injured in an attack on the US embassy in the capital on Friday by protesters.

"Three protesters were shot dead, the fourth was hit by a car and 49 people were injured, including nine seriously," a spokesman for the ministry told AFP on Saturday.