Fighters from the Moro Islamic Liberation Front (MILF) on southern Basilan island "will defend themselves to the death," rebel spokesman Eid Kabalu said.

"They will live and die in Basilan. The MILF is prepared for any eventuality, while staying on a defensive mode," Kabalu told AFP by telephone from his base in the southern Philippines.

Armed forces chief General Hermogenes Esperon had given the MILF until the end of Sunday to turn over those behind the deaths of the Marines, 10 of whom were beheaded and mutilated, or face a military offensive.

The Marines were on a search mission for kidnapped Italian priest Giancarlo Bossi when they were ambushed by MILF rebels, allegedly assisted by al-Qaeda-linked Abu Sayyaf militants.

Bossi, who was freed Thursday, has said he was never on Basilan during his ordeal.

The 12,000-strong MILF, which has a three-year-old truce in place, admits its forces attacked the marines after they entered MILF territory without advance notice, but denies any role in the beheadings.

Although he repeated the denial on Sunday, Kabalu said any MILF forces found to be involved in the beheadings would be punished by the rebels themselves, and not turned over to the government.