The attack occurred early Tuesday off Malaysia's west coast, said Noel Choong, head of IMB's Kuala Lumpur-based piracy reporting centre. The diesel oil tanker was believed to be en route to Myanmar.
"IMB is aware of the attack on the Singapore-managed ship in the Malacca Straits. IMB is concerned about the kidnapping of the three senior Indonesian crew members," he told AFP, adding that the ship was now berthed off Port Klang, Malaysia's main port, for investigations.
The Star daily, quoting a district police officer, reported that the incident occurred shortly after midnight about 16 nautical miles off the coast, and the crew only realised when they saw about five or six men armed with a pistol and a machete aboard the ship.
The report said the pirates subdued and tied up the crew, robbed the vessel and brought in two other tankers that pumped out a large quantity of the vessel's diesel.
After the attackers fled several hours later, the crew discovered three shipmates were missing.
Police suspect they were kidnapped by the pirates, the report said.
The crew comprised Indonesian, Thai, Myanmar and Indian nationals.
No further details on the vessel were provided.
Choong said in previous attacks in the region in recent years, pirates had mostly stolen cargo but not kidnapped any crew members.
The Strait of Malacca is a key highway for sea traffic between and Asia, Europe and the Middle East, and has long been a hunting ground for pirates due to the large numbers of cargo and other vessels passing through.
Attacks in the region had dropped in recent years following stepped up patrols and cooperation between neighbouring countries to secure waterways.
But they have surged again with the Southeast Asian region reporting the highest number of incidents last year, especially smaller-scale robberies of crew members on board off Indonesia, according to the IMB. (AFP)
