Four Sri Lankan fishermen have died and another two are critically ill after consuming an unknown liquid from bottles they found while at sea, according to local media reports.

The sailors were said to be on a fishing trip when they retrieved the bottles around 320 nautical miles from Tangalle, a town on the southern coast of the island.

The Sri Lanka Navy told reporters the fishermen had drunk from the bottles thinking they contained alcohol.

Director General of the Sri Lankan Department of Fisheries and Aquatic Resources, Susantha Kahawatte, told several outlets that the navy was attempting to bring them back to shore.

He reportedly said that the the navy was providing medical attention to the men aboard the fishing vessel - named the Devon - over concerns there was not enough time to return them to land for treatment.

The BBC has approached Mr Kahawatta and the Sri Lanka Navy for confirmation and comment.

Mr Kahawatta told national news station Ada Derana that the fishermen had distributed some of the bottles to other crews operating in the area.

He added that attempts to notify these crews were being made.

The navy told local media that the Devon was being towed back to shore by another vessel. It set off from Tangalle on 4 June.

The incident has reportedly prompted protests in the coastal town - located around 120 miles (193km) from the capital, Colombo - calling for the sailors who were still alive to be returned to land.

Authorities are now investigating the contents of the bottles.