MANILA (AFP) - Ten Muslim extremists were killed Wednesday in a fierce firefight with government troops on the southern Philippine island of Basilan, the military said.

The death toll could be higher as troops continue to hunt down members of the Abu Sayyaf extremist group who were behind the kidnapping of three local school teachers four months ago, said Captain Neil Estrella.

The group released the teachers on Tuesday, possibly after a ransom was paid.

Estrella said once the safety of the schoolteachers was assured, Marines began "stalking the perpetrators."

They encountered the main body of about 50 Abu Sayyaf members before dawn Wednesday, leading to an intense firefight, he said.

The bodies of 10 Abu Sayyaf members were recovered with no casualties on the government side.

While the fighting has subsided, pursuit of the extremists is continuing, said Estrella.

The Abu Sayyaf are known for kidnapping Christians and foreigners for large ransom payments and have killed their hostages when their demands have not been met.

Earlier this month, the Abu Sayyaf in Basilan beheaded a retired Christian carpenter abducted two months earlier after his family failed to pay a ransom.

Another group of Abu Sayyaf militants continue to hold Italian Red Cross worker Eugenio Vagni on the island of Jolo, where they kidnapped him in January. Two other Red Cross workers abducted with Vagni have since been freed.

The Abu Sayyaf was founded in the 1990s, ostensibly to fight for an independent Islamic state in the southern Philippines. Intelligence agencies say they have links to the Al-Qaeda terror network.

The United States on Tuesday offered up to 2.5 million US dollars in rewards for tips leading to the capture of three senior Abu Sayyaf members.