A senior leader of the Muslim rebel group the Abu Sayyaf has been shot and possibly killed, according to Philippine government officials.

Abu Sabaya and two of his men are believed to have been killed during a gunfight at sea with troops, military officials say.

The bodies are yet to be found but four other rebels who were captured confirmed that their leader was one of three men who jumped off the sinking boat near the coast of southern Zamboanga peninsula.

Major-General Ernesto Carolina said divers had recovered sunglasses like those worn by Abu Sabbaya, a satellite phone and a backpack from the sea.

"I don't have any doubt this is (only) a matter of getting the body of Sabaya from the water," he said.

If Abu Sabaya's death is confirmed it will be a major blow to the rebel group, which is notorious for carrying out kidnaps for ransom.

Hostage-taking is the group's main activity although its stated aim is the creation of an independent Muslim state in the south of the mainly Christian Philippines.

The US believes the group has links with Osama Bin Laden's al-Qaeda network. In May it put a $5m bounty on the head of Abu Sabaya, along with four other leaders.

Friday's shootout happened when special forces intercepted a boat carrying armed men off the coast of Sibuco in the southern province of Zamboanga del Norte province.

Defence Department spokesman Major-General Melchor Rosales said navy commandos returned fire at the suspected rebels, sinking their boat.

A number of the suspected rebels were hit and jumped or fell overboard.

Celebrity

General Rosales said the four wounded men who were rescued from the sinking boat were "verified Abu Sayyaf" and were being interrogated.

Abu Sabaya:

Real name Aldam Tilao Aged 40 Former police trainee Former member of Muslim separatist Moro National Liberation Front (MNLF) Quit MNLF when it signed '96 peace treaty Spent time in Saudi Arabia Returned to Philippines in '99 Trademark dress: black bandana and sunglasses

The BBC's John McLean in Manila says Abu Sabaya is something of a national celebrity because of his habit of calling local radio stations on his satellite phones to taunt the authorities.

He and his men had been holding two American missionaries, Martin and Gracia Burnham, and a Filipina nurse Ediborah Yap for more than a year.

An operation mounted by the Philippine military on 7 June rescued Mrs Burnham but the other two hostages were killed in the fighting.

US troops have been helping to train local soldiers to fight the guerrillas for several months.

Washington, which sees the campaign against Abu Sayyaf as part of its war on terror, has offered a reward of up to $5m for the capture in the Philippines of the rebel leaders, including Abu Sabaya.

The group is led by the reclusive Khadafi Janjalani, the brother of founder Abdurajak Janjalani who was killed by troops in 1998.