The Liberation Tigers of Tamil Eelam, which has raised security concerns by becoming the world's first insurgent group to use air power, might be working on acquiring underwater vessels that could pose a threat to merchant shipping in regional waters.

Reports have suggested that the LTTE, which has a naval wing called the Sea Tigers, is building a mini-submarine as part of its new arsenal.

A top Indian Navy official, who was asked about this issue on Thursday, did not discount it entirely and said the LTTE could be 'trying its hand' at building 'submerged vehicles.'

To questions about the possibility of the LTTE acquiring a submarine and how big a threat this will pose to India and its neighbourhood, Rear Admiral Pradeep Chuahan said the threat will be as good or bad as threats posed by any terrorist group operating on land.

Chauhan, the assistant chief of naval staff at naval headquarters in New Delhi, however, noted that submarine building and operating such vessels are very complicated matters.

"You cannot make or operate submarines by opening manuals," he said, asserting that surveillance and patrolling had been intensified in Palk Strait and adjoining seas.

The Indian Navy also plans to set up a facility at Ramanathpuram on the Tamil Nadu-Kerala border, a region where it currently has no major base.

The LTTE's fledgling air force carried out a strike on a military airbase near the international airport in Colombo on Monday, killing three persons.

"There are very few countries in the world that can claim to have the capability to build and operate submarines," Chauhan said.

On operations in the Palk Bay area, Chauhan said India and Sri Lanka were conducting 'coordinated patrols' to cope with the emerging threats.

Elaborating, he said it was not a joint or combined operation but a coordinated exercise.

"The Sri Lankan Navy patrols its own waters while the Coast Guard patrols Indian shores. The results have been pretty encouraging," he said.