Documents related to terror outfit LeT have allegedly been recovered from two of the arrested men, who are said to be members of banned outfit Ansarullah Bangla Team (ABT).
The two other arrested persons are an Indian arms dealer and a Bangladeshi citizen, who helped people cross the international border illegally.
"Coastal security has been enhanced. As it is, regular patrolling is carried out in the area to prevent any infiltration through the sea route," Commodore Suprobho K De, Naval Officer-in-Command, Bengal area, told reporters.
De said joint exercises involving the Navy, Coast Guard, Intelligence Bureau, state police and other stakeholders were periodically held to ensure preparedness in the region in view of the 26/11 Mumbai attack, where the terrorists had come through the sea route.
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"Very proactive measures are being taken by all the agencies and the security has been beefed up in the region," he added.
De said there were many security challenges in the Sunderbans region, the largest mangrove forest of the world situated in the Gangetic delta, such as arms, fake currency, drugs smuggling, human trafficking, illegal migration etc.
As such, keeping a vigil on the ground and the numerous rivers that criss-crossed the forest was a viable option for tracking any such activity, he added.
De said the Navy Day would be celebrated at INS Netaji Subhas, the naval headquarters in West Bengal, on December 4 to commemorate the attack by the Indian Navy on the Karachi harbour on this day during the 1971 Indo-Pak war.