Tamil Nadu Chief Minister J. Jayalalithaa has urged the Indian government to undertake a strong diplomatic offensive against Sri Lanka to stop it from arresting Indian fishermen.In a letter of Prime Minister Narendra Modi released to the media on Friday, Jayalalithaa said: "I have repeatedly emphasized the importance of the government of India undertaking a strong diplomatic offensive to uphold the rights and interests of Indian fishermen from Tamil Nadu."Urging Modi's personal intervention in securing the release of Indian fishermen in Sri Lankan jails, Jayalalithaa said a total of 73 fishermen and 101 fishing boats were in the island nation's custody."I urge that there should be strong and decisive action by the government of India in this matter and the present situation cannot be allowed to fester in this manner," Jayalalithaa said.She said on July 7, 16 Indian fishermen in mechanised fishing boats from Rameswaram were apprehended by the Sri Lankan Navy, taking the number of fishermen in Sri Lankan custody to 73.India and Sri Lanka are divided by a narrow strip of sea. Sri Lankan authorities frequently arrest Indian fishermen, accusing them of fishing in Sri Lankan waters.