Chennai, Aug 23 : Three Tamil Nadu fishermen from Nagapattinam were attacked and robbed in mid-sea by unidentified persons. Fishermen said that the incident occurred on August 22, several nautical miles away from the Kodiyakkari coast while they were fishing. The fishermen have been identified as Vaithanyathaswamy, Selvaraj and Ramaraj -- natives of Vellappallam in Nagapattinam district. The three returned back to the coast on Wednesday early morning to Vedaranyam coast. Police said that six unidentified persons in two boats intercepted the Tamil Nadu fishermen mid-sea and assaulted them using wooden logs and also stole their signal lights. The fishermen complained that their GPS system, gadgets, mobile phones and fish catch were stolen by the assailants. This is the second such incident reported this week in mid sea. On August 21, fishermen from Vellapallam and Arcottuthurai coastal villages alleged that they were assaulted by a group of unidentified men some nautical miles from Arcottuthurai coastal village. Fifteen persons who suffered injuries are under treatment at hospitals in Nagapattinam and Vedaranayam. Coastal Security Group sources told IANS that cases were filed against unidentified Sri Lankan nationals under Section 397 (dacoity, robbery with attempt to cause grievous injury) of the Indian Penal Code. /IANS