About half a dozen soldiers took Education Minister Chaturon Chaisang into custody in a chaotic scene at the Foreign Correspondents' Club of Thailand, where he had just finished giving a surprise news conference.
The junta, which seized power Thursday, is already holding most top members of the Southeast Asian country's elected administration and has ordered the rest to surrender.
Chaturon called for elections and warned that resistance to the army overthrow could grow, which could lead to "a disaster for this country."
When the news conference was finished and Chaturon was being interviewed by a group of Thai journalists, soldiers entered the room, surrounded him, and escorted him out through a crowd of reporters. He was calm and smiling as he was taken away.
Before being hustled into an elevator, Chaturon said: "I'm not afraid. If I was afraid, I wouldn't be here."
The military takeover, Thailand's second in eight years, deposed an elected government that had insisted for months that the nation's fragile democracy was under attack from protesters, the courts, and finally the army.
The country is deeply split between an elite establishment based in Bangkok and the south that cannot win elections on one side, and a poorer majority centered in the north that has begun to realize political and economic power on the other.
A "coup d'état is not a solution to the problems or conflicts in Thai society, but will make the conflicts even worse," Chaturon said.
Chaturon said he told only a few people in advance of his appearance. He said he would not resist arrest or go underground, but since he does not "accept the coup, I could not report to those who staged it."
"I still insist to use my own rights and liberty to call for returning the country to democracy," he said.
After declaring martial law May 20, Gen. Prayuth Chan-ocha invited political rivals and Cabinet ministers for two days of peace talks to resolve the crisis. But those talks lasted just four hours. At the end of the meeting, Prayuth ordered everyone inside detained, and announced the army was seizing power on state television almost immediately afterward.
Prayuth, who was endorsed Monday by the king as the nation's new ruler, warned opponents not to criticize or protest, saying Thailand could revert to the "old days" of turmoil and street violence if they did.
Still, small numbers of protesters have gathered on Bangkok streets in defiance of martial law. Several hundred people gathered Monday at Victory Monument and eventually dispersed on their own, vowing to return on Tuesday.
The junta has ordered 258 people to report to the authorities so far. Among them are scholars, journalists and political activists seen as critical of the regime.
It is unclear how many are in custody, but some have been released, including former Prime Minister Yingluck Shinawatra, who had already been forced from power by a court ruling before the putsch took place.
Others are being summoned daily, and some have fled or are in hiding. Human rights groups describe a chilling atmosphere with soldiers visiting the homes of perceived critics and taking them away in the night.
Prayuth said the army was taking people into custody to give them time "to calm themselves down" and none was being tortured or beaten. "When summoned, they will be asked about what they've done. ... If they are calm and still, they will be released."
Chaturon called the detentions "absurd" and said "they are taking people who have done nothing wrong just because they might resist the coup."
"The problem is, we don't know how long they are going to be detained," he said. "I'm worried more about the people who fight for democracy and the academics. ... We don't know what happened to them. We don't really know."
Chaturon dismissed speculation that members of the ousted government and their allies could form a government-in-exile. But warned that "from now on there will be more and more resistance. ... It will be a disaster for this country."
He did not elaborate.
The junta has yet to map a way out of the crisis, but Prayuth has said there would be political and administrative reforms. On Monday, he gave the green light for the Finance Ministry to seek billions of dollars in loans to pay debts owed farmers under a disastrous rice scheme instituted by the ousted government.
The junta has given no timetable for restoring civilian rule, and Chaturon said Prayuth "might want to hold onto power for some time."
Prayuth, he said, has "assigned the generals to take care of the jobs at the ministries - the tasks they know the least."