The Indian Coast Guard ship Vaibhav apprehended the Lankan boat. The Coast Guard personnel also apprehended six crew members of the boat, sources in TN police said here.
Apart from the heroin, 20 small packets of synthetic drugs, possibly meth, were also seized.
Initial investigation reveals that the drugs were transferred to the Sri Lankan boat from a Pakistani dhow from Karachi.
The heroin packets were kept hidden in an empty fuel tank of the vessel. The Coast Guard team had been keeping a vigil on boats for more than a week before zeroing in on the Lankan fishing vessel, Shenya Duwa.
During initial questioning, the Lankan crew disclosed that the drugs were transferred into their vessel on the high seas by a Pakistani dhow from Karachi.
The boat is allegedly owned by one Deeptha Sani Fernando from Negombo, Sri Lanka.
The arrested crew members were taken to Thoothukudi port and are being questioned by teams from Central and state agencies to know if there were any possible recipients from TN who could be of part of the international drug smuggling network.