JAKARTA • Indonesia yesterday freed a Singapore-flagged vessel captured by pirates off the coast of Borneo island and detained nine suspects involved in the hijacking, a navy spokesman said.

The 20 crew members and one passenger who were aboard the captured boat were unharmed during the operation, navy spokesman Edi Sucipto said in a statement.

The vessel had disappeared from radar inside Indonesian waters before reappearing some distance away under a different name, arousing suspicion.

Commodore Sucipto said the navy pursued the vessel before securing it and freeing the captive crew. The pirates had planned to shift 200,000 litres of oil from the Singapore- flagged ship to another vessel, he added.

Nine Indonesian citizens were detained on suspicion of piracy and were being transferred to Surabaya city, in the north-east of Java island, for further questioning.

Indonesia has vowed to protect its vast archipelago from illegal incursions by unregulated fishermen and pirates, and has seized hundreds of vessels in a tough crackdown.

"The Indonesian navy will continue to patrol the seas to maintain safety within Indonesian territory," Commodore Sucipto said.

Piracy is common along South-east Asia's lucrative maritime trade routes.

Indonesian President Joko Widodo has called for Indonesia, Malaysia and the Philippines to look into holding joint patrols to combat the threat of piracy in regional waters.

Separately, Malaysian Defence Minister Hishammuddin Hussein last month said Singapore and Thailand could be involved as "observers" in patrolling the Sulu Sea area, while Malaysia, the Philippines, Brunei and Indonesia work on trying to resolve the piracy menace.

AGENCE FRANCE-PRESSE