Prominent Thai journalist Pravit Rojanaphruk, who is the first journalist to be summoned by the military junta, has reported to the army.
"I believe the Thai people will keep up the struggle for freedom and democracy," Mr Pravit, a columnist with Thailand's second largest English daily The Nation, said briefly to a few reporters gathered at the gates of the army office on Sunday morning.
The junta, which seized power on Thursday, has summoned close to 200 people including politicians and academics.
Among the first to report to the junta on Friday was former prime minister Yingluck Shinawatra who is now under detention along with several other members of the government that was ousted by army chief General Prayuth Chan-ocha.
"I hope the Thai people keep up the spirit," Mr Pravit said. "I hope today's dictator General Prayuth is the last dictator for Thailand."
Shortly after he spoke, troops burst out of the gate to politely but firmly shoo the media away. Mr Pravit went in, accompanied by two United Nations observers and a lawyer.
Mr Pravit, regarded as progressive because he has often written about and discussed Thailand's harsh lese majeste law which hands down long jail terms to anyone deemed to have insulted the King, Queen, heir or regent, was the subject of a specific summons issued late on Saturday.
The junta has launched a widening purge, with General Prayuth imposing martial law, detaining politicians and activists, suspending the constitution, abolishing the Senate and assuming all lawmaking powers. It has said those summoned but failed to report to it will be prosecuted.
The army has also raided homes and offices of figures in the "red shirt'' movement, and arrested several. Many more have gone underground.
Under martial law, the army has the power to detain anybody for seven days without charge or warrant. To extend the detention, charges have to be filed in a court.
Martial law also bans gatherings of more than five people - a regulation already being tested by angry Thais in Bangkok and Chiang Mai who have taken to the streets in small groups to protest the coup d'etat. Some of the protests have been quiet, using candle light.
But some have turned raucous with protesters chasing and pushing at soldiers, with more serious incidents only narrowly averted on Friday and Saturday.
More protests are planned in Bangkok on Sunday. Armed troops which have intensified their presence at the upscale, downtown Rachaprasong intersection where a noon protest is planned, were seen dragging off three protesters.
The United States, which has designated Thailand a non-Nato ally, has suspended military aid, cancelled an ongoing joint military exercise and an upcoming visit to Thailand by US Pacific Fleet Commander Admiral Harry Harris, and recalled an invitation to the Thai armed forces' Supreme Commander General Tanasak Patimaprakorn to visit the US Pacific Command in June.
"We are increasingly concerned about actions the Thai military has taken, just a few days after it staged a coup... We again call on the military to release those detained for political reasons, end restrictions on the media, and move to restore civilian rule and democracy through elections," US Department of State Deputy Spokesperson Marie Harf said in a statement.