Ten Indonesian sailors abducted by Abu Sayyaf militants were freed in the southern Philippines on Sunday after five weeks in captivity, Philippine police said.

Unknown men dropped off the 10 tugboat crewmen at the home of provincial governor Abdusakur Tan Jnr on the remote island of Jolo during a heavy midday downpour, Jolo police chief Junpikar Sitin told AFP by telephone.

"The report (of their release) is confirmed. They were there. I saw them," Superintendent Sitin added.

The condition of the former captives was not immediately known, though Sitin said the group ate lunch at the governor's home.

They were abducted on March 26 by gunmen described by Philippine authorities as members of the Abu Sayyaf, a small group of militants based on Jolo and nearby Basilan island which is accused of kidnappings and deadly bombings.

The militants are reported to have sought a ransom, but Sitin said he was unaware that any had been paid. Abu Sayyaf does not normally free hostages unless a ransom is paid.

The Indonesians were freed six days after Abu Sayyaf members beheaded a Canadian hostage, John Ridsdel.

Philippine President Benigno Aquino vowed Wednesday to neutralise the militants after Ridsdel's decapitated head was left outside a government building on Jolo.

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The authorities said the group is still holding 11 other foreign hostages – four Indonesians, four Malaysians, another Canadian, a Norwegian, and a Dutchman.

Abu Sayyaf is a radical offshoot of a Muslim separatist insurgency in the south of the mainly Catholic Philippines that has claimed more than 100,000 lives since the 1970s.

It is believed to have just a few hundred militants but has withstood repeated US-backed military offensives against it, surviving by using the mountainous, jungle terrain of Jolo and nearby islands to its advantage.

Abu Sayyaf gangs have earned many millions of dollars from kidnapping foreigners and locals since the early 1990s.

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Although Abu Sayyaf's leaders have pledged allegiance to Islamic State, analysts say they are more focused on lucrative kidnappings-for-ransom than setting up an Islamic caliphate.