Four-nation joint aerial patrols will be launched next week over the Malacca Straits as part of efforts to counter threats of piracy and terrorism in the vital waterway, Indonesia said today.

The "eye in the skies" air patrols would be launched next Tuesday after signing that day of an agreement by the defence ministers from Indonesia, Malaysia, Singapore and Thailand in Subang, Malaysia, said Navy Colonel Surya Wiranto.

The three littoral states of Malaysia, Indonesia and Singapore have already begun coordinated sea patrols of the waterway, but agreed last month to boost surveillance with joint air patrols.

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 straits, 960 kilometres long and 1.2 kilometres wide at its narrowest, is vulnerable to pirate attacks and governments in the region also believe it is a tempting target for terrorists.

Wiranto said the air surveillance scheme, originally proposed by Malaysia, would involve up to two maritime patrol aircraft from each nation that would operate seven days a week.

The aircraft, which must have one military officer from each participating nation on board, would be allowed to fly above waters of the four nations no less than three nautical miles from land.

"If Indonesia is unable to send (a representative), then those airplanes will not be allowed to enter our territory. The principal of sovereignty will remain in place," said Wiranto, an operational assistant with the Indonesian navy's western fleet.

Radar surveillance system

Speaking on the sidelines of a two-day meeting on security issues in the strait, Wiranto said further details of the scheme were still being hammered out.

The meeting earlier witnessed the signing of an agreement between Indonesia, Malaysia and Singapore and the International Maritime Organisation and various international shipping operators to place a radar surveillance system along the straits.

Thai Prime Minister Thaksin Shinawatra said last Saturday after talks with Singapore's premier Lee Hsien Loong that he supported the joint air patrol initiative and would consider further contributions to security in the region.

Lee said although Thailand was not a littoral state of the waterway, it was situated on its northern approaches and could become involved in protecting the area.