MANILA (AFP) - Three Philippine soldiers were killed in a major assault on a Muslim extremist camp in the southern Philippines, the military said on Wednesday (Dec 16).

The battle, involving as many as 150 members of the Abu Sayyaf group, was continuing for a third day on Wednesday, according to the military, which also reported several militant deaths that could not be verified.

The operation began after a large number of armed men were seen in a suspected Abu Sayyaf stronghold in a forested part of Basilan island, about 885km from Manila, said Major Filemon Tan, the regional military spokesman.

"We are using artillery bombardment, rocket barrages from MG-520 helicopters and armoured vehicles," Tan told AFP.

"The enemy is using booby traps so our troops have to be very careful."

Up to 350 soldiers, including rangers, marines and special forces, were involved in the assault, Tan said.

Reports from villagers and frontline troops indicated about 15 members of Abu Sayyaf had been slain and seven wounded, Tan said, although he said no bodies had been retrieved.

He said three soldiers had died and 11 were wounded.

Tan said the military was still trying to capture the camp, but declined to give further details to avoid compromising their operations.

Basilan, an impoverished island of about 400,000 people, has long been a stronghold of the Abu Sayyaf, a group founded in the 1990s with the help of Al-Qaeda founder Osama Bin Laden.

Abu Sayyaf is infamous for kidnapping people, including foreigners and demanding huge ransoms for their release.

Security forces fear that a Norwegian, two Canadians and an Italian kidnapped in separate incidents in the south earlier this year may have been taken by various Abu Sayyaf factions.

Tan said there were no signs of any hostages in the fighting so far.

The decapitated head of a Malaysian man kidnapped by the Abu Sayyaf in May was found last month on the southern island of Jolo, another Abu Sayyaf haven near Basilan. The rest of the body was found only this week.

The group has also been blamed for the worst terror attacks in the country, including the firebombing of a ferry off Manila Bay in 2004 that killed over 100 people.

Last year, Abu Sayyaf leaders pledged allegiance to the Islamic State group, which controls vast swathes of Syria and Iraq.