KUALA LUMPUR (AFP) - A Thai tanker is thought to have been hijacked on its way from Singapore to Indonesia, the International Maritime Bureau said on Saturday, following a number of pirate attacks in Southeast Asian waters.

The diesel oil tanker MT Orapin 4, with 14 crew aboard, lost contact with its owner after departing the city-state on Tuesday, IMB's Kuala Lumpur-based Piracy Reporting Centre said. It was heading to Pontianak on Indonesia's Kalimantan.

"It's a possible hijacking," the centre's head Noel Choong said, adding that pirates recently had attacked a number of vessels in the area, usually to siphon off cargo. The centre urged other vessels to keep a look-out for the missing tanker.

In April, heavily-armed pirates boarded another Thailand-owned tanker off the eastern coast of Malaysia, injuring the captain and stealing diesel fuel from its cargo.

In the same month, pirates also boarded a Singapore-managed tanker in the nearby Strait of Malacca, an important shipping lane, kidnapping three Indonesian crew and stealing some of the diesel fuel.

January to March saw 23 actual or attempted attacks in Southeast Asian waters, mainly off Indonesia, according to IMB.