Abu Sayyaf gunmen killed six soldiers who were guarding a road project that has been delayed by militant attacks in an impoverished southern Philippine province, the military said.
The soldiers were patrolling the outskirts of a farming village in Sumisop town on the island province of Basilan when about 20 heavily armed Abu Sayyaf fighters opened fire, sparking a 45-minute battle, army Col Rolando Bautista said.
At least one soldier also was wounded. It was not immediately clear if there were rebel casualties.
The Abu Sayyaf, which is on a US list of terrorist organizations, was founded in the early 1990s in Basilan, a predominantly Muslim province in the majority Catholic nation, about 880 kilometres (550 miles) south of Manila.
Despite many battle setbacks, the group has endured, surviving mostly on kidnappings and extortion, and remains a national security threat.
Bautista said he deployed additional troops to pursue the attackers, who were led by a commander he identified as Radzmi Jannatul.
The attack came as hundreds of troops hunted down Abu Sayyaf gunmen on nearby Jolo island, where the militants freed two German tourists last month reportedly after a huge ransom payment.
