Thai police said that more than 21,000 suspected drug users or traffickers had been arrested in the first two weeks of a nationwide crackdown.

Police have conducted thousands of searches since December 21, after the government ordered action to tackle the problem.

The authorities seized 1.6 million methamphetamine pills, 40.4 kilograms of heroine, 295 kilos of marijuana, and 8.5 kilos of crystallised methamphetamine, also known as ice.

Altogether the drugs have an estimated street value of 500 million baht ($16.5 million).

Thailand, along with other countries in the region, has seen a marked increase in seizures of methamphetamine as the world opiate trade declines.

Police said they had also seized 345 guns, 1,175 bullets, and six grenades during the operation, which is due to last one month.

- AFP