The suspects were disguised as fishermen, navy spokesman Chaminda Walakuluge said.
"Drug smugglers operate disguised as fishermen," Walakuluge told AFP. "We are on alert for drugs coming in."
He said the navy has seized a total of 130 kilos (286 pounds) of heroin and cocaine and 2,140 kilos (4,708 pounds) of cannabis in the past year and arrested a total of 19 Indians during the same period.
Last week, Sri Lankan Navy arrested 12 Indian fishermen from Tamil Nadu, prompting the state government to ask the centre to send an "unequivocal message" to Colombo to stop the apprehensions.
In 2014, Sri Lanka sentenced five Indian fishermen to death for drug smuggling, but they were later released into Indian custody.
The killing of an Indian fisherman last month along the maritime boundary led to widespread protests in Tamil Nadu.
(With inputs from AFP and PTI)