Clashes between troops and suspected Al Qaeda-linked militants have killed at least 57 people and wounded 42 others on volatile southern Jolo island this week, the Philippine military said Friday.

The death toll included 25 soldiers and 27 militants killed Thursday when suspected Abu Sayyaf extremists ambushed a truck carrying troops headed to get supplies, then fought a running gunbattle with soldiers in pursuit, said Lt. Col. Bartolome Bacarro, the military's spokesman.

"As far as I can remember, this is our biggest casualty in a day," Bacarro told reporters.

Ten soldiers and 25 militants were wounded in Thursday's clashes, he added.

Early Thursday, the insurgents ambushed members of the army's 33rd Infantry Battalion who were on their way to get supplies in Indanan township, killing 10 soldiers and wounding another, Bacarro said.

Late in the afternoon, troops from the same battalion encountered about 120 Abu Sayyaf militants and rogue members of the Moro National Liberation Front, a rebel group that signed a peace agreement with the government 11 years ago, Bacarro said.

Heavy fighting broke out and running skirmishes, backed by four military attack helicopters, left 15 more soldiers dead and nine wounded.

"Based on validated intelligence reports, there were 27 killed on the ASG (Abu Sayyaf Group) side and 25 wounded, he said.

Maj. Eugene Batara, spokesman for the military's Western Mindanao Command in southern Zamboanga city, said soldiers recovered the bodies of five slain rebels, while the rest of the dead and wounded were carted away by their comrades.

The militants were led by Abu Sayyaf commanders Albader Parad, Dr. Abu Pula, and Radullan Sahiron, an elusive one-armed commander long wanted by U.S. and Philippine authorities for his alleged role in several terror attacks, officials said.

"Out of these killed ... we are trying to verify reports that one is the son of Dr. Abu and one was a close aide of Radullan Sahiron," Bacarro said.

The skirmishes on the island began earlier in the week. On Tuesday, two platoons of troops clashed with about 50 Abu Sayyaf members in Indanan township, wounding two marines.

The next day, army troops engaged the militants in a 30-minute fire fight in Parang township, killing one soldier and wounding five others. The Abu Sayyaf suffered four dead.

"All in all ... starting from the Aug. 7 encounter ... till late last night, the Armed Forces of the Philippines suffered 26 killed in action and 17 wounded in action," Bacarro said. "About 31 ASG (members) were killed and 25 wounded."

The military is pouring in two more battalions to augment forces on Jolo, bringing the total number of troops in Sulu province to 4,000, he added.

"We will continue and press our effort in ... tracking down these high-value targets," Bacarro said. "We know their locations and we will continue pressing and hopefully we'll be able to engage them again."

Sulu provincial Governor Sakur Tan said he has instructed the mayors of Maimbung and Indanan townships to prepare evacuation centers for residents who may flee due to the conflict.

The military estimates that Abu Sayyaf, which has been blamed for deadly bombings and high-profile ransom kidnappings, has about 300-400 guerrillas, down from more than 1,000 during its heyday in early 2000.

Batara said Thursday's ambush was not an indication that the Abu Sayyaf has regained strength following setbacks dealt by a massive U.S.-backed offensive last year that led to the killing of its top two leaders.

"They've been attacking our soldiers when they're not in battle mode," Batara said. "They could not fight frontally. They're treacherous."