The Philippine army is battling Muslim rebels who it says are making a "last stand" after a week of clashes on the southern island of Jolo.
The military shows no sign of agreeing to a ceasefire
Up to 12,000 people have fled the fighting which has left about 90 soldiers and rebels dead.
The rebels are from the al-Qaeda-linked Abu Sayyaf group along with followers of the jailed militant, Nur Misuari.
Between 4,000 and 5,000 troops are fighting 800 militants in the heaviest fighting for years.
The fighting began last Monday. An Abu Sayyaf leader, Abu Solaiman, told a radio station it had joined forces with the Misuari followers to avenge the death of a couple and their son who were killed by troops.
The military says it returned fire after the couple shot at soldiers.
The rebels then attacked troops at an army base, killing 30, including the battalion commander, the military says.
The government flew in reinforcements, including US-trained counter-terrorist troops, and said the army has killed more than 60 rebels in heavy fighting.
Three more soldiers were killed on Sunday as they pursued the militants, the army said.
"There's heavy fighting going on in the Panamao and Luuk areas," said senior southern Philippines commander Lt Gen Alberto Braganza.
"They are taking a last stand in the mountains."
Anti-terrorist taskforce commander, Brig Gen Agustin Dema-ala, said: "We are still encountering resistance but the situation is manageable."
Absalom Cerveza, a Misuari ally, said he had spoken to the rebels on Friday and they were in "high spirits and far from being crushed".
Misuari was jailed after a failed uprising in 2001
"They do not like to surrender, they will fight to the death," he said.
The BBC's Sarah Toms in Manila says there have been local calls for a ceasefire but the army has shown no signs it will agree.
Misuari was the founder of the Muslim separatist Moro National Liberation Front (MNLF).
The MNLF signed a peace deal with Manila in 1996 under which Misuari became governor of an autonomous region.
But he mounted a failed rebellion when he was not endorsed for a second term and fled to Malaysia. He was deported and jailed.
Abu Sayyaf has been involved in a number of kidnappings and bombings. It was blamed for sinking a ferry in Manila Bay last year, killing more than 100 people.
Although the Jolo fighting is the worst since Misuari's uprising in 2001, the military has never been able to bring Jolo under full control.
The rebels hold much of the island with support from many of the residents.