The Malaysian police have arrested two crewmen from a tanker which was hijacked by pirates this week, saying they believed it was an inside job, according to reports today.

Ten Indonesian pirates boarded the tanker off Langkawi island on Tuesday but their planned attack was foiled when a quick-thinking sailor raced off in their speed boat, stranding them on the vessel.

He returned with five police patrol boats and after a tense standoff, the pirates aboard the Malaysian tanker were coaxed into surrendering.

Kedah state police chief Mohamed Supian Amat told The Star that an Indonesian crew member and another unidentified officer were believed to have alerted the pirates to the ship which was travelling from Singapore to Burma.

"We believe this is an inside job. This hijacking was well planned," he told the English-language daily.

Beaten and abused

The New Straits Times quoted other crew members as saying that while they were beaten and abused by the 10 Indonesian pirates, the two men under suspicion were not treated roughly or rounded up with the others.

The Malacca Straits is one of the world's most important waterways, with 50,000 ships carrying about one-third of the globe's trade passing through it each year.

However the strait, 960 kilometres long and 1.2 kilometres wide at its narrowest point, is notoriously vulnerable to pirate attacks and governments in the region also believe it is tempting for terrorists.