Sri Lankan police arrested four people on Friday, including a Pakistani national, after seizing 50 kilos (110 pounds) of high-grade heroin with a street value of one million dollars.

The drugs were found packed in a container of potatoes in the port of Colombo, police spokesman Prishantha Jayakody said.

Most drug seizures take place at Sri Lanka's international airport, but the Police Narcotics Bureau believes a substantial number of shipments, mostly heroin from India and Pakistan, are smuggled in by sea.