Defence officials in Indonesia, Malaysia and Singapore have increased sea and air patrols in the Straits of Malacca, after Singapore authorities warned that attacks were being planned in the area's shipping lanes.
The latest threat was said to target an oil tanker, but few details have been given.
The Malacca Strait is one of the busiest shipping lanes in the world. Half the world's oil is transported through it and hundreds of vessels pass through every day.
The shipping route is highly vulnerable, as a bottleneck of just 2.7km leaves little room for ships to manoeuvre or gather speed.
According to security analysts, the region is well-placed to detect and deter any threat, but doubts remain over whether maritime authorities would be able to thwart an attack without air and land support.
Al Jazeera's Laura Kyle reports from Singapore (09 Mar 2010).
Source: Al Jazeera