Apichart Punnajanto, a Buddhist monk who has posted online videos that harshly denounce Islam, has been detained by the authorities.
Pol Col Dusit Promsin said Apichart was detained in Songkhla on Tuesday by officers from the Crime Suppression Division.
The monk was taken into custody because of videos he had posted online, Pol Col Dusit said. He did not describe the content.
Thai media published images of temple records showing Apichart was expelled from the monkhood on Wednesday night at Wat Benjamabophit in Bangkok.
Sunai Phasuk, senior researcher on Thailand for Human Rights Watch, criticised his detention in a Twitter post. He said it was more proof that under the ruling military junta, "everyone risks becoming a victim of freewheeling uses of power, secret detainments, and unlawful prosecutions".
Apichart has spoken out on many issues, but is best known for posting a suggestion that a mosque be burned down anytime a monk is killed by Muslim separatist insurgents in the deep south.
He also recently renewed a feud with a government religious official, saying in a video that he filed a defamation suit against him and sarcastically urging people in the South, to where the official was recently transferred, to give him a "warm welcome".
The Cross Cultural Foundation, a rights group active in the South, also called for Apichart's immediate release, while adding it does not support actions by religious leaders that instigate conflict among religious groups.