On Monday, Riot police broke up a rally held outside the Myanmar embassy in Bangkok and arrested a Thai protester. At least two people were reportedly injured.
About 150 riot police were called into the area on Sathon Road to disperse the protest against the military coup in Myanmar.
A police source said a security guard was arrested, but Piyarat "Toto" Chongthep of the We Volunteer (WeVo) Thai pro-democracy group posted a message saying at least three people were detained.
Police estimated 200 Thai activists, 100 WeVo members, and 100 Myanmar supporters of Suu Kyi had gathered outside the embassy on Sathon Road to condemn the coup in the neighboring country and demand the Thai government do likewise.
"Thailand must not endorse and legitimize this coup — as well as coup government," WeVo said in a statement.
"We affirm that as a member of ASEAN, we cannot stay silent after such an evil and unlawful act."
The Myanmar army detained National League for Democracy Party leader Aung San Suu Kyi and other politicians on Monday morning before announcing a one-year emergency state, with former Gen Myint Swe appointed as acting president.
Deputy Prime Minister Prawit Wongsuwon said the coup was an "internal affair" of Myanmar.
But Mr. Chongthep, the WeVo activist, disputed that notion, saying, "We never accept a coup -- no matter who [launches] it."
Parit "Penguin" Chiwarak, a vital member of the United Front of Thammasat and Demonstration, said the two countries' situations were quite similar as Thailand has also spent years under military dictatorship.