Abu Sayyaf has been blamed for bomb attacks in the south, kidnappings-for-ransom and beheading of captives, including an American citizen in 2001.
Two members of the Philippine Coast Guard taken hostage by al Qaeda-linked militants three months ago have escaped captivity during a raid by U.S.-trained commandos on a remote southern island, an army spokesman said on Thursday.
Four other hostages, including two businessmen from Malaysia and South Korea, held at the same location in the jungle near Indanan town on Jolo island have still not been accounted for, army spokesman Captain Antonio Bulao said.
He said security forces had killed 15 members of the Abu Sayyaf group late on Wednesday during the rescue operation.
The two coast guardsmen took advantage of the confusion during the firefight and escaped.
"They are here with us and having a meal right now," Bulao told reporters by phone from an army base on Jolo. "They are in high spirits but tired after hiding all night before they were found today.
"We have no word if the other four captives were able to run away from the rebels," he said, adding the offensive on Jolo to free all hostages, including another Malaysian, a Dutch national and a Japanese national, would continue.
"The order from headquarters was to rescue all of them."
Abu Sayyaf has been blamed for bomb attacks in the south, kidnappings-for-ransom and beheading of captives, including an American citizen in 2001. The rebels are led by Yasser Igasan, seen as having close links to al Qaeda.
Since 2002, a small U.S. military contingent has been training and advising Philippine forces in fighting Abu Sayyaf and two other militant groups - the Bangsamoro Islamic Freedom Fighters and a small group claiming affiliation with Islamic State.