Board deputy secretary-general Chartchai Suthiklom said yesterday that a change in supply routes from the North to the Northeast had been detected.

Drug Prevention and Suppression Centre director and Defence Minister General Boonrawd Somtas heard yesterday that anti-narcotics efforts had reduced the volume in circulation during Songkran.

This included methamphetamine, marijuana, heroin, cocaine and designer drugs, Chartchai said.

Almost 261,000 methamphetamine tablets were seized in April. That is a third of the haul in March. Most - 57 per cent - is brought into Thailand via Northeast borders whereas smugglers had used the North for eight of 10 shipments previously.

More than 700 kilograms of marijuana smuggled from Laos via Nong Khai and Mukdahan were seized in April - an increase on March. Heroin seizures in Mae Hong Son and Chiang Mai totalled almost eight kilograms - down substantially on the 35 kilograms seized the previous month.

Two kilograms of cocaine were confiscated from a Peruvian smuggler stopped while entering Thailand at Suvarnabhumi Airport, Chartchai added.

Drug-related arrests and seizures in urban areas are on the rise, accounting for 43.5 per cent of all cases. Those in Bangkok accounted for 22 per cent of the total.

Drug-related cases in the deep South were 9 per cent of the total - a reduction on 12 per cent in March.

Chartchai said drug-related offences were reported in three-quarters of the provinces. In March there were cases in 67.5 per cent of provinces.

Authorities have put 28 provinces on their blacklist, including Bangkok, Chiang Mai, Nakhon Ratchasima, Khon Kaen, Pathum Thani, Nakhon Si Thammarat, Songkhla, Narathiwat and Yala.

There will be a combined board and police crackdown on methamphetamine abuse in Bangkok starting this month and running until September.

Yesterday's meeting heard that militants in the deep South were abusing a mixture of cough syrup and Kratom leaf, or Mitragyna speciosa, as a stimulant ahead of insurgent action.