A third of global crude oil shipments pass through the Malacca Strait
Singapore has learned that an unnamed group may be planning to attack oil tankers in the Malacca Strait, one of the world's busiest shipping lanes.
"The terrorists' intent is probably to achieve widespread publicity and showcase that they remain a viable group," the country's navy warned.
Other large vessels with dangerous cargoes were also at risk, it said.
The navy recommended ships strengthen their onboard security measures, remain vigilant and report unusual incidents.
Past cases of successful attacks on tankers were carried out using small vessels such as dinghies, speedboats and fishing boats, which are common in the Malacca Strait, the Navy advisory said.
About 33% of global seaborne crude oil shipments pass through the 965km (600-mile) channel - which is shared by Malaysia, Indonesia and Singapore.
The seaway is almost six times busier than the Suez Canal.
A Singapore Navy spokesman could not provide further details of the new threat when contacted by the Bloomberg news agency, but said it had started "operation co-ordination with our regional partners".
Malaysia's maritime enforcement agency said it was aware of the alert and was stepping up security in the shipping lane.
American sailors on watch while transiting through the Strait of Malacca. 

The Singapore Navy on Thursday warned of a possible pirate threat to ships passing through the Strait of Malacca after receiving a correspondence from an unnamed terrorist organization.

According to the Navy, the intent of the terrorists was to "achieve widespread publicity and showcase that they remain a viable group." While the threat received covered only oil tankers, other large cargo ships were also at risk of attack, naval officials went on to say.  

To reduce possible risks, the Navy urged ships to strengthen onboard security, including adding additional lights and lookouts. They also recommended that ships maintain a higher speed and report any unusual incidents to the proper authorities. The advisory said that past attacks in the Strait had been carried out by small vessels such as motorboats or fishing boats with armed crews. Commercial vessels were also warned to avoid known fishing areas accordingly.

The Singapore Navy said that it had contacted other countries in the area to warn them of the threat. Both Indonesia and Malaysia have also announced plans to increase patrols in order to provide additional security.

The Strait of Malacca is a major conduit for oil shipments. With around a third of global oil shipments passing through, it is the main route for travelling from the Middle East to Asia. Any attack on vessels within the Strait would likely have a major ripple effect on global trade.