The suspects who were arrested on Friday were Phairoj Mahanil, 28, Thongchai Kantha, 29, Thassanai Thamrongchiwin, 23, and Suchart Thamrongchiwin, 24, it was announced at a press conference at the Narcotics Suppression Bureau in Bangkok yesterday.

Pol Maj General Thanai Apichartsenee, who led the operation, said police received tips-off that a gang would travel to Tachilek, across from Chiang Rai, to smuggle in the drugs.

Police spotted a Hyundai van crossing to Tachilek at 6.30pm on Friday and returning through the Mae Sai border checkpoint, driven by Phairoj and following a Toyota Yaris. When the car occupants spotted a checkpoint in Phitsanulok, the van stopped at a hotel. A police check found drugs in a hidden compartment. Police later arrested three other suspects in the car.

Thongchai allegedly said he was hired for Bt200,000 to deliver the drugs to a customer in Nonthaburi and that his gang had smuggled drugs to Bangkok and Phitsanulok.

Meanwhile, highway police in Khon Kaen province foiled an attempt to smuggle 530 kilograms of marijuana with a street value of Bt10 million into Bangkok early yesterday.

Acting on tips-off, police set up a checkpoint on the Mitraparp Road in Tambon Sa-ard of Nampong district from midnight.

At 2.20am, they spotted a pickup truck with a covered load and waved for it to stop, but the driver sped off. After a 10-kilometre chase by police, the driver pulled over on a forest verge. Bags of marijuana were found in the truck.