(AFP) The fight against crime on the high seas is threatened by a new trend, that of pirates demanding ransom for the release of kidnapped crew members, an international piracy watchdog said today.

The International Maritime Bureau Piracy Reporting Centre here said there had been two such cases within two months in northwest Indonesian waters near Aceh on Sumatra island.

"The IMB believes that there may be more cases which have gone unreported due to owners being threatened and warned not to report to the authorities," the centre said in report covering the first nine months of 2001.

It noted that the Free Aceh Movement had threatened to disrupt shipping in the Straits of Malacca between Sumatra and Malaysia as part of its fight for an independent state.

"The Indonesian armed forces insist that the group lacks the resources for any meaningful blockade. The navy is to double its patrols in the area," the report said.

The centre advised captains to be extra cautious in the area and avoid anchoring along the Indonesian coast of the Malacca straits.

'Use tracking system'

Shippers were advised to install the "Shiploc" tracking system which can be used to trace and recapture hijacked vessels.

The centre said there had been a total of 253 actual and attempted attacks on ships worldwide in the first nine months of this year.

Indonesian waters were by far the worst, accounting for 71 of the attacks.

An earlier report by the centre attributed the growth in piracy in the area partly to political unrest and economic turmoil in Indonesia.

Malaysia recorded 15 actual or attempted attacks, Bangladesh 19 and India 22.

Apart from Asia, the centre singled out Somalia's waters for a specific warning over hijackings and advised ships to keep at least 50 nautical miles from the coast of the African country.

"Armed pirates in speed boats and gun boats open fire on ships/yachts and rob or hijack them. Some crew have been injured or killed in the past," the report said.