The emergency decree restricts transport, publication of "sensitive news" and gives police and soldiers authority to resolve the "emergency situation." The move follows anti-government protests in Bangkok.
Thailand's prime minister, Prayuth Chan-ocha, signed an emergency decree on Thursday, forbidding public gatherings of over five people and restricting transport.
The decree also bans the publication of "sensitive news" and gives police and soldiers authority to resolve the "emergency situation."
Prayuth cited "aggression affecting the state's stability" for the move, after anti-government protests escalated on Wednesday night.
"It is extremely necessary to introduce an urgent measure to end this situation effectively and promptly to maintain peace and order," Prayuth said. It is not clear for how long this emergency decree will be in effect.
Another reason cited for the emergency measure was the obstruction of a royal motorcade by the protesters on Tuesday.
Some have also made controversial calls for reforms to the monarchy — long considered a sacrosanct part of Thai identity.
The decree took effect at 4 a.m. local time, after which police occupied the streets where protesters were present. In total 15,000 officers were deployed in the city ahead of the demonstrations planned for Thursday at a major commercial intersection in Bangkok.
Police said they had arrested over 20 activists including protest leaders Anon Nampa and Parit Chiwarak.
Anon said in a Facebook post that he had been forced aboard a helicopter to Chiang Mai in northern Thailand without a lawyer present. He claimed he will face sedition charges for a speech he delivered during a protest in August.
"This is a violation of my rights and is extremely dangerous to me," he wrote on Facebook.
It remains unclear how those arrested were accessing their social media accounts.
Thousands of people marched to the Government House on Wednesday to demand the resignation of the ex-army chief turned prime minister, Prayuth Chan-ocha.
The protests took place on the anniversary of a student uprising on October 14, 1973 that led to the toppling of a military dictatorship.
Last month, tens of thousands of pro-democracy protesters turned out in Bangkok in one of the country's largest rallies in years.
Activists argue that Prime Minister Prayuth, who toppled an elected government in a 2014 coup, manipulated last year's general elections to ensure the military stayed in control — a charge he denies.
The protesters are also calling for curbs on the constitutional powers of the king and for him to transfer back the control he took of some army units. However, these public demands have been met with a backlash from the royalist establishment.
Under Thailand's royal defamation law, criticism of the monarchy is punishable with up to 15 years in prison.
kmm, am/dr (Reuters, dpa, AFP)