"While the Centre showed active and keen interest in taking up at all levels the killing of two Kerala fishermen, it is painful to see it taking a soft approach toward Sri Lankan Naval personnel who constantly harass the Tamil Nadu fishermen," he said.
Mr Karunanidhi, whose party pulled out from the ruling UPA last month on the Sri Lankan Tamils issue, said it would not be wrong to expect the Centre to take a "fair and reasonable" approach without any differentiation between Tamil Nadu fishermen and their Kerala counterparts.
Noting that there has been sudden spurt in the attacks on Tamil fishermen by Sri Lankan Navy, Mr Karunanidhi, writing in his party organ "Murasoli" said, such an approach by the Lankan Navy was "highly condemnable".
He said it was also not "wrong" to seek from Tamil Nadu Chief Minister J Jayalalithaa measures in protecting the state fishermen as done by her Kerala counterpart Oommen Chandy, who he said took "active efforts" over the marines' issue.
Mr Karunanidhi's statement comes in the backdrop of the recent arrest of Tamil Nadu fishermen by Sri Lankan Navy in the last two days and seizure of their boats on charges of fishing in the island nation's waters.