Security patrols in the Malacca Strait have increased following a warning from Singapore that terrorists were planning attacks on ships.
Defense authorities in Indonesia, Malaysia, and Singapore say they have increased sea and air patrols in the Malacca Strait.
Singapore warned that a terrorist group was planning attacks on oil tankers in the shipping lanes, through which half the world's oil and much of its trade is transported.
The warning did not specify a terrorist organization or say when the sea attacks were expected. But, the Singapore Navy said militants could use small boats to launch the attacks and urged shipping companies to stay alert for suspicious activities.
Rohan Gunaratna, the head of the International Center for Political Violence and Terrorism Research in Singapore, says the countries are right to take the terrorism warning seriously.
"Malacca Straits is one of the busiest ports in the world. And, if there is an incident in Malacca Straits that it can have a very significant impact on global trade and commerce. So, it is so important for governments to take warnings very seriously," he said.
The Singapore Navy's Information Fusion Center said terrorists may be planning attacks to seek publicity and show that they are still active.
Gunaratna says al-Qaida and Jemaah Islamiya are two of the terrorist groups likely behind the warning.
"Terrorism poses a continuing threat in the region. Certainly the incidents of maritime attacks have been fewer. But, in this case there's a specific warning, a specific threat alert, pertaining to maritime attack," he said.
Pirates have used small boats to hijack ships in the Malacca Strait. But, maritime policing by Indonesia, Malaysia, and Singapore has reduced the threat from piracy.
Terrorism however remains a concern.
Indonesian police on Thursday charged 14 suspects with planning terrorist attacks after a raid on a suspected militant training camp in Aceh province.
Indonesian police say the men are believed to have links to Jemaah Islamiya.
Aceh is at the north end of the Malacca Strait.
But it is not clear if those arrested in Indonesia were related to the terror warning issued by Singapore.