SINGAPORE - About 3.7kg of heroin and 1kg of cannabis were found in a Malaysia-registered bus at Woodlands Checkpoint on Thursday (May 4).

After directing the bus for further checks, Immigration & Checkpoints Authority (ICA) officers found a suspicious bag at the right side of the driver's seat, the ICA and Central Narcotics Bureau (CNB) said in a joint news release on Friday (May 5).

The 36-year-old Malaysian bus driver was arrested, along with two of his passengers - a 20-year-old man and a 24-year-old man.

Officers from CNB seized a total of about 3.7kg of heroin and 1kg of cannabis. The drugs are worth an estimated $307,000.

In a follow-up operation, CNB arrested the intended recipients of the seized drugs - a 35-year-old woman and a 48-year-old man, both Singaporeans.

They were arrested in the Jalan Pelatok area, off Upper Changi Road East.

A raid of the suspects' rented room there uncovered a total of 260g of "Ice" or methamphetamine, 130g of heroin, two "Yaba" or methamphetamine tablets, a small amount of cannabis and a bottle of methadone.

Investigations are ongoing.

Under the Misuse of Drugs Act, the suspects can face the death penalty if more than 15g of diamorphine or pure heroin is trafficked.

ICA and CNB in their release said Singapore's borders are the country's first line of defence in safeguarding Singapore's security, and that security checks are critical to the nation's security.

"The Home Team agencies will continue to conduct checks on passengers and vehicles at the checkpoints to prevent attempts to smuggle in undesirable persons, drugs, weapons, explosives and other contrabands," they said.