According to officials, Sri Lankan naval men assaulted the fishermen using rubber pipes and wood before asking them to get into their boats and sped away.
Three boats in which they had put out to sea returned here with the drivers.
Normally Sri Lankan navalmen would arrest the fishermen along with their boats. It was not known why they let off the boats and the drivers, Police said.
Marine Police alleged that the Sri Lankan Navalmen intruded into the Indian waters near the fifth sand dune.
Police said they were interrogating the boat drivers.
