A combined team of military police, forest officials and members of the Sukhothai provincial Buddhism office raided Sri Intharatit forest monastery in Moo 3 of Thung Saliam subdistrict.
They served a warrant for the arrest of Phra Anupan Saksua, 34, for allegedly building a monastery, a sawmill and a garage on land that is part of Tham Lom-Tham Wang Forest Park.
The team detained Phra Anupan and took him to the ecclesiastical district governor of Thung Saliam to be expelled from the monkhood, shortly after the raid.
Army Capt Jirapat Sonsakul, of the Phitsanulok Military District peacekeeping force, who led the operation, said authorities would shut down the monastery and dismantle the illegal structures on the land.
They were also examining several cars found parked in the garage to see if they had been used to hide illegal items. The abbot claimed they had broken down and the engines would not start.
An initial investigation indicated the vehicles had been frequently driven to Chiang Rai, Lampang and Mae Sot border town in Tak, which were areas used by smugglers transporting drugs from neighbouring countries, Capt Jirapat said.
The team would also investigate some forest park officials suspected of being involved in the encroachment, he added.