Superintendent of Police Mayilvahanan said there was information that eight terrorists plan to infiltrate by sea and coastal people have been advised to inform police in case they saw any strangers.
Patrolling of coastal areas has been intensified since last night, he said.
Officials said the IB alert has been conveyed to all units of the Intelligence wing, Coast Guard and Naval personnel.
Coast Guard officials said two hover crafts, two small ships and a big ship from Chennai have been deployed in the Palk Strait to monitor the sea to prevent infiltration.
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An Indian naval helicopter has also been engaged. Police said they had given a telephone number, 1093, to all hamlets in the coastal areas to enable people inform police in case any stranger comes in the guise of fishermen.
The SP said vigil has been intensified from Mandapam to Rameswaram, and security for Rameswaram temple where people from north India come in large numbers, tightened.