By Roy Ramos & Hader Glang

ZAMBOANGA CITY, Philippines

Philippine authorities are verifying whether a boat abandoned along the coast of southern Sulu – an island province known as a stronghold of an al-Qaeda-linked militant group -- was used in a recent abduction.

Brig. Gen. Alan Arrojado, Joint Task Group Sulu commander, said Saturday that police found the outrigger boat Friday off the coast of Parang town, some 300 nautical miles from Davao del Norte province, where three foreigners and a Filipina were kidnapped Monday.

“Elements of the Parang MPS [Municipal Police Station] are still at the area securing the craft while waiting for the water to rise [to high tide] in order to tow the sea craft,” he said in a statement. “Accordingly, the sea craft bore some holes that caused seawater to leak inside.”

He cited a police report describing the yellow-orange boat with white and blue stripes as being approximately 25 meters long and 2.5 meters wide with balancers or outriggers.

He said that there had, however, been no sighting or information as to the whereabouts of the hostages – Canadians John Ridsel and Robert Hall, Norwegian Kjartan Sekkingstad, and Filipina Teresita "Tess" Flor.

Unidentified armed men forcibly took Sekkingstad, 56; Ridsdel, 68; Hall, 50; and Tess -- said to be Hall’s fiancée -- from the Holiday Ocean View Samal Resort on Samal Island at around 11 p.m. (1500GMT) Monday.

Meanwhile the mayor of Davao City, located to the west of Samal, said Saturday that he had received intelligence information that the hostages had been taken to Sulu.

Rodolfo Duterte told ABS-CBN News that the kidnap gang had passed by Glan, Sarangani province, to the south – from where it took only six hours to reach Sulu.

He declined to identify the group responsible for the abduction but said they may be linked to the Abu Sayyaf since a suspect caught on security footage appeared to resemble a known member of the militant group.

"They [victims] were delivered to a known Abu Sayyaf Group. Whether they [kidnappers] are also actually Abu Sayyaf members, that we do not know,” he said. “It's expected as they are passed from one group to another, the ransom is expected to go up."

He expressed his belief that the targets were pre-determined, and reiterated his willingness to be part of the team negotiating their release.

However, ABS-CBN News also quoted Chief Supt. Federico Dulay, head of the National Police’s Special Investigation Task Group Ocean View, as saying they believe the kidnappers have not left the Davao Region.

A military source who requested anonymity as he was not allowed to speak to media told Anadolu Agency that a group known as “Tanum” – which means plant or sow in the local Tausug and Bisaya dialects – was behind the kidnapping. Tanum is also a village in the Sulu town of Patikul.

According to intelligence information, the Tanum group caught media attention in past years for carrying out abductions for the Abu Sayyaf.

Kidnap-for-ransom gangs frequently operate in Zamboanga Peninsula and the island provinces of Sulu, Basilan and Tawi-Tawi.

The gangs are known to hand over their captives to the Abu Sayyaf and negotiate for a ransom that, if paid, is shared with the group.

The kidnappers use isolated sea-lanes and coastal areas to grab their victims, who are then held captive in isolated Muslim villages in the peninsula.

Since 1991, the group -- armed with mostly improvised explosive devices, mortars and automatic rifles -- has carried out bombings, kidnappings, assassinations and extortions in a self-determined fight for an independent Islamic province in the Philippines.

It is notorious for beheading victims after ransoms have failed to be paid for their release.