A total of 14.6 million methamphetamine tablets were seized in a crackdown on drug trafficking carried out on a road running along the Mekong River in Wiang Kaen district of Chiang Rai in the early hours of Monday.

The operation was carried out by a combined force of military rangers, soldiers, officers from the Mekong Riverine Unit of the navy and local administrative officials at about 1.30am following a report that a major drug smuggling operation was being planned in this Thai-Lao border area.

The river serves as a natural border separating Thailand from Laos.

The force spotted two pick-up trucks approaching and waved for them to stop for inspection. However, all of the occupants fled their vehicles under the cover of darkness, said Maj Gen Wichit Wongsang, chief of the Pha Muang task force in Chiang Rai.

Some 73 sacks were seized from the two cars, yielding 14.6 million meth tablets, he said.

Police are tracking the network believed responsible, he added.

In related news, police seized 12.5 million baht in cash during a raid on a house owned by Prathip Yachina, who was arrested with 10 million meth tablets and 100 kilogrammes of crystal meth in Ayutthaya on Saturday.

The house is in Chiang Rai's Mae Sai district. When the raid took place on Sunday night, Mr Prathip's wife -- who has not yet been identified by name -- was reportedly present.

The cash was kept in two safes. The raid was carried out by a combined force of soldiers from the Pha Muang task force, local police and officials from the Narcotics Control Board's Region 5 office.

Army chief Gen Apirat Kongsompong has ordered a stepped-up drug suppression operation from next month until January as trafficking is expected to intensify.