Shipowners have been warned to be vigilant after a spate of pirate attacks in the Bangladeshi port of Chittagong, an international watchdog said today.

The International Maritime Bureau (IMB) recorded at least 18 attacks since January 28 this year, the head of the Malaysia-based Piracy Reporting Centre, Noel Choong, told AFP .

"Basically there have been 18 attacks in Chittagong since 28 January 2006, but we believe many more may have gone unreported," said Choong.

"We believe that there are groups of pirates operating in the area. We are warning ships that enter the area to be extra vigilant. We are concerned about the high number of attacks in that location."

Choong said the IMB had written a letter to the Bangladesh authorities urging them to take the necessary action and to increase patrols in the affected area.

The IMB had also issued a warning to all shipping entering Chittagong, via its satellite broadcast, he said.

"We would like to see more action being taken with the pirates. It would be a more effective deterrent," he said.

Four of the attacks occurred this month.

Other incidents

On May 9, a Liberian bulk carrier anchored at Chittagong was boarded by 10 men armed with knives, said Choong. They took three men, including one crewmember hostage and robbed them, before fleeing in a speedboat.

On May 10, another gang attempted to rob the same vessel but failed.

On May 12, a Caribbean cargo ship was boarded by five armed men but they escaped after the alarm was raised.

Later the same day, a group of seven men stole the stores from a Caribbean bulk carrier after boarding it using grappling hooks.