The Philippine military is sending reinforcements to the restive southern Island of Jolo, where fighting between government troops and Muslim rebels has been raging all week.
The military says it now has about 4,000 soldiers targeting at least 800 loosely organized militants on Jolo.
The government says two Muslim rebel groups are represented among the militants: Abu Sayyaf, a group linked to al-Qaida, and renegades from the larger Moro National Liberation Front, or MNLF.
The military says nearly 30 soldiers and about 60 militants have been killed since a rebel ambush sparked the violence last Monday.
Julkipi Wadi is a professor of Islamic Studies at the University of the Philippines with strong ties on Jolo.
He says recent government operations on the island may have precipitated Monday's ambush. He says rebel leaders accuse the army of shooting local villagers during a raid last week.
"That escalated the problems, because the military said those civilians were Abu Sayyaf members," he explained, "but according to people they are ordinary civilians, so that resulted in the retaliation by the MNLF forces in the area."
The violence, which has also displaced nearly 3,000 families, is the worst since a rebel uprising in 2001.
Abu Sayyaf and the MNLF renegades both have strongholds on Jolo, one of a string of islands that stretches across the Sulu Sea between the southern Philippines and the island of Borneo.
President Gloria Arroyo said Thursday the fighting will not stop the government from seeking a lasting peace with rebel groups in the Southern Philippines.
Muslims, who form a large part of the southern population of the Philippines, have been fighting for an independent state for nearly three decades.