Philippine marines clashed for a second day Tuesday with al-Qaeda linked militants holding three Red Cross workers hostage, killing at least six combatants and wounding 19 troops, officials said.

There was no word about the fate of the hostages — a Swiss, an Italian and a Filipino — held for more than two months but their agency, the International Committee of the Red Cross, expressed concern that a military rescue could harm them.

The fighting erupted Monday when Abu Sayyaf gunmen led by Albader Parad attempted to break out of a loose cordon set up by government forces to box in dozens of militants and their hostages in a hilly jungle near southern Jolo island's Indanan township.

The military said Parad may have been wounded by marine snipers but there was no immediate confirmation.

Fighting resumed Tuesday, leaving three militants and three marines dead and 19 troops wounded, said military spokesman Brig.-Gen. Gaudencio Pangilinan and Jolo Governor Abdusakur Tan.

"They are desperate. They want to get out of the constriction area," Pangilinan told reporters, referring to the Abu Sayyaf gunmen.

'Their safety is paramount'

Red Cross officials late Monday expressed worry that the hostages — Swiss Andreas Notter, Filipino Mary Jean Lacaba and Italian Eugenio Vagni — could be harmed by military action to try to free them.

"Their safety is paramount. We repeat our call that no action should be taken that could put [their lives] in danger," Alain Aeschlimann, head of ICRC Southeast Asia-Pacific operations, said in a statement.

The workers were kidnapped Jan. 15 after inspecting a Jolo jail water project.

So far, military officials have refrained from rescuing them to ensure their safety and to allow local officials to negotiate their safe release.

The Abu Sayyaf, however, has demanded that the military back off from its stronghold before any negotiation can take place. The government has rejected any such demands.

Tan, who heads a task force overseeing the hostage crisis, said he had not authorized a military rescue but added troops can open fire if the militants attempt to escape from the jungle area or if Abu Sayyaf gunmen attack.

"Anytime they attempt to escape, we'll engage them," Tan told the Associated Press by telephone. "It's clear that the Abu Sayyaf is feeling the pressure of the military presence."

U.S. and Philippine officials have offered a reward for the capture or killing of Parad, a young militant who has gained notoriety for alleged involvement in past kidnappings and beheadings.

Last month, Parad acknowledged on television that his group was holding the Red Cross workers.

The Abu Sayyaf has about 400 members and is on a U.S. list of terrorist organizations for its links with al-Qaeda and involvement in kidnappings, bombings and beheadings.

Officials say the guerrillas may have resorted to a rash of kidnappings to raise badly needed funds after they lost most connections to foreign financiers when many of their commanders were killed in U.S.-backed offensives.