Sri Lankan police have arrested 24 Indian fishermen, adding to the 112 already in custody for allegedly straying into Sri Lankan waters.
The Indians were seized by a group of local fishermen and handed over to police.
The arrests have sparked protests in southern India and were condemned by Indian Prime Minister Manmohan Singh, who said they were unacceptable.
Diplomats are in talks to try to secure the fishermen's release or bail.
"This sort of behaviour is not acceptable between neighbouring countries," the Indian leader said on Wednesday.
The incident is the latest development in a continuing row over fishing rights.
The two countries now have a "joint working group" on fishing but it seems it has a lot of work to do to prevent such incidents recurring, says the BBC's Charles Haviland in Colombo.