Residents of Jolo Island rescued the trapped man, a regional military spokesman said on Wednesday.

"The victim escaped when his captors declared that they would behead him," Major Filemon Tan said.

The island is a known stronghold of the Abu Sayyaf militant group. The militiamen had previously moved the hostage to a mangrove area in the island's Luuk town, some 1,000 kilometers (620 miles) south of the Philippines' capital Manila.

"We were told he managed to escape by running and swimming to the sea," Tan added.

Abu Sayyaf kidnapped the 28-year old sailor Mohammad Sayfan along with six other Indonesian tugboat crewmembers in June. Weeks later, the group allegedly took three more Indonesian fishermen.

Duterte speaks out

The group specializes in kidnapping foreign citizens and demanding high ransoms. According to family members of the kidnapped sailors, they were demanding $5 million (4.7 million euros) for the tugboat crew's release.

In May, the militia released a separate group of 14 Indonesian sailors after holding them for several weeks. Jakarta denied paying any ransom.

The guerillas are also believed to be holding hostages from Malaysia, Norway, the Netherlands and Japan. Two Canadians were beheaded after Ottawa declined to pay ransom.

Sailing through the busy waters between Indonesia and the Philippines has grown increasingly risky as Abu Sayyaf has kidnapped dozens of people in the area.

Philippines President Rodrigo Duterte has called for a "day of reckoning" with the group. On Tuesday, he also condemned the Abu Sayyaf's practice of cutting the throats of hostages.

"I do not know how to meet this kind (of barbarism), but if you do that, you bring out the worst in me," the "Philippine Star" quoted him as saying. "If you can do it, I can do it ten times better than you."