Singapore's navy is urging commercial ships passing through a major shipping lane that runs between Indonesia and Malaysia to increase security measures.
The navy said a terrorist group is planning attacks on oil tankers travelling through the Strait of Malacca. The strait is a major trade route, and an attack that closes it could have a major impact on global trade.
"The terrorists' intent is probably to achieve widespread publicity and showcase that it remains a viable group," an advisory said. "However, this information does not preclude possible attacks on other large vessels with dangerous cargo."
They didn't say which terrorist group is planning the attacks.
The Malacca Strait is the favorite route of oil shippers between the Persian Gulf and Asian Pacific markets. The strait, just 2.7 kilometers at its narrowest point, was the second-busiest shipping lane of crude in 2006, with 15 million barrels a day passing through, according to the U.S. Energy Information Agency.
Singapore lies at the southern tip of the Malay peninsula and is home to the world's busiest port.
Indonesia has not received any information from Singapore about possible attacks but plans to boost air and sea patrols, Defense Ministry spokesman Brig. Gen. I Wayan Midio said.
"We are committed to increase the awareness and security in the Malacca Strait to anticipate any terrorist attacks," he said.
Singapore said small fishing boats or speedboats were used in past successful terrorist attacks against ships, and these kinds of vessels could be used in the Malacca Strait.
They recommended ships add lookouts and lighting, avoid fishing areas and maintain a good speed. Spokesmen at the Defence Ministry were not immediately available for comment.