The operation, involving 23 teams of 506 police, was launched on information that about 22 drug suspects had used Ayutthaya as their base for the drug trade in Bangkok and nearby provinces as well as in the Central and Northeast regions in coordination with drug convicts in Klong Phai Prison in Nakhon Ratchasima's Si Khiu district.
In a raid on a house in Rom Ruen housing estate in tambon Chiang Rak Noi of Bang Pa-in district, the police arrested Nathawat Tingchairoj, 34, and seized 140,000 meth pills.
Acting on information from Nathawat, the police arrested three other suspects - Chaiyuth Natworathat, 32, Wassana Paopang, 22, and Arisa Kingngern, 27 - with 28,000 speed pills.
In Nakhon Phanom, seven men were arrested with 252 kilogrammes of compressed marijuana on the bank of the Mekong river.
Pol Lt Col Chusak Thavornpoj, the That Phanom police chief, said the seven men were arrested at about 4am with the marjuana, smuggled from Laos, on the bank of the Mekong river at Ban Khap Phuang in tambon Nam Kam.
The police also seized two pickup trucks and three motorcycles used by the seven suspects, who were initially charged with smuggling drugs into the country with intent to sell.