Malaysian police have detained four Thais and a Malaysian whose fishing vessel is suspected of involvement in a pirate attack on a Japanese tugboat in the Malacca Straits, a spokesman said today.

"We detained the fishing boat on Thursday. The five crew members are being questioned now. The boat is alleged to have been used in the attack," said Mokhtar Othman, operations officer for Malaysia's northern region marine police.

Mokhtar said the registration number of the Malaysia-registered boat was the same as that on one of the craft involved in Monday's attack in which two Japanese officers and a Filipino crewman were kidnapped.

Mokhtar said the remaining crew of the tugboat and the barge it was towing were expected to attend an identification parade to see if the detained suspects were involved in the attack.

The pirates, who are suspected of planning to make a ransom demand, had not yet communicated with the Japanese ship owners, he said.

Mokhtar said the marine police were under intense pressure to locate the kidnap victims and arrest the pirates and were working closely with their Indonesian counterparts.

"Since it involves international nationals, the focus is on us to resolve the issue," he said.

M'sia-registered boats in attack

The strait, which carries a third of world trade and half its oil supplies separates peninsular Malaysia and Singapore from Indonesia's Sumatra island, providing the quickest route from the Indian Ocean to the South China Sea.

The US ambassador to Malaysia said today Washington was concerned about piracy and the potential for terrorism in the strait and was prepared to help secure the vital shipping lane if asked.

"Obviously, all of us are concerned about the increase over the period of time in pirate attacks. We must be concerned about potential for terrorists to also operate somehow in the strait," Christopher J La Fleur was quoted as saying by the official Bernama news agency.

"The US obviously has various sorts of military capability and if asked, of course we will be happy to consult with countries in the region on this issue."

Malaysia has repeatedly rejected the involvement of forces from the United States or other foreign governments in patrolling the shipping lane, saying it would infringe on its sovereignty and attract rather than repel terrorism.

Outsiders unwelcome

Indonesia also insisted today that outsiders were unwelcome on patrols in the strait because security was the responsibility of Indonesia, Malaysia and Singapore.

"Indonesia's position is clear. We believe that the responsibility for maritime security in the Malacca Straits belongs to the littoral states, including Indonesia," foreign ministry spokesman Yuri Thamrin told reporters.

Singapore's Defence Minister Teo Chee Hean said yesterday in Jakarta that Japan was considering a role in multinational patrols in the strait.

Thamrin said that while such a move was unwanted, Indonesia would welcome assistance aimed at strengthening its navy.

La Fleur agreed that the three littoral states had the primary responsibility of dealing with pirate attacks.

"If there are ways that we can help, then certainly we are prepared to talk."

Third pirate attack in two weeks

The Japanese tugboat was on its way from Indonesia's Batam island to Burma when the pirates kidnapped 56-year-old captain Nobuo Inoue, 50-year-old chief engineer Shunji Kuroda and Filipino crewman Sangdang Paliawan, 31.

It was the third pirate attack on shipping in the Malacca Straits within two weeks.

Last weekend a gang of 35 pirates armed with machine guns and rocket launchers boarded the Indonesian-registered gas tanker Tri Samudra and kidnapped the captain and the chief engineer.

The kidnappers have already demanded a ransom of two billion rupiah (RM916,000) from the owners, Humpuss Intermoda Transport.