Indonesian authorities have voiced concerns that piracy in the Sulu Sea area, a major sea traffic lane for the worlds top thermal coal exporter, could reach levels previously seen in Somalia.
Analysts say $40 billion worth of cargo passes through those waters a year, including supertankers from the Indian Ocean that cannot use the crowded Malacca Strait.
"We got confirmation (yesterday) of an incident of kidnapping involving Indonesian crew of a ship," Indonesian Foreign Minister Retno Marsudi told reporters. She said the hijackings were carried out by two different armed groups in attacks on a tugboat towing a coal-carrying barge.
Six of the 13 crew on board were freed, Marsudi said, and were on their way back to Indonesia.
"We absolutely do not tolerate this. The government will try all options to free the hostages," Marsudi said.
Up to 18 Indonesians and Malaysians were kidnapped in three attacks on tugboats earlier this year in Philippine waters by groups suspected of ties to the Abu Sayyaf militant network. All 14 Indonesian citizens were later released.
The Philippine military has said the militants have been targeting foreign crew of slow-moving tugboats because they can no longer penetrate resorts and coastal towns in Malaysias eastern Sabah state due to increased security.
The rise of sea hijackings prompted Indonesia, the Philippines and Malaysia to agree last month to carry out coordinated patrols to secure the regions busy waterways.
However, coordinated patrols are yet to get underway.
Abu Sayyaf, known for amassing tens of millions of dollars from kidnappings, has beheaded two Canadian nationals in recent weeks after ransom deadlines passed.
The group is still holding Malaysian seamen and Japanese, Dutch, Norwegian, and Philippine citizens.(*)