Thai police said on Monday they had ordered an investigation of four news outlets under emergency measures imposed last week to try to stop three months of protests against the government and monarchy.
The announcement prompted anger from media groups and accusations of an attack on press freedom by the government of Prime Minister Prayuth Chan-ocha, the former junta leader the protesters are seeking to drive from office.
According to a police document dated October 16, investigations have been ordered into content from four media outlets as well as the Facebook page of a protest group.
"We received information from intelligence units concerned that parts of the content and distorted information have been used and disseminated to cause confusion and instigate causing unrest to society," police spokesman Kissana Phathanacharoen told a news conference.
He said it was for Thailand's broadcast regulator and digital ministry to investigate and take appropriate action, adding that there was no plan to curb press freedom.
Putchapong Nodthaisong, a spokesman for the digital ministry, said it had requested court orders to take down content by the four media outlets and a protest page, among more than 300,000 pieces of content it said violated Thai laws.
Prachatai, an independent outlet among those being investigated, described it as a censorship order.
"Honored to report accurate info about human rights and political development in Thailand, we'll try our best in continuing to do so," Prachathai English said on Twitter.
The Manushya Foundation, an independent group which campaigns for online freedom, called the measures an attempt to silence free media.
"Since the ban on protests did not work, the military-backed government hopes to create fear of telling the truth," its director Emilie Palamy Pradichit said.
"We urge free media to resist."
The government ordered a ban on news and online information that could affect national security last Thursday as it also banned political gatherings of more than five people in the face of the growing challenge.
Protests have taken place every day since then, the latest drawing tens of thousands of people in Bangkok and across the country. Police gave a figure of 20,000 protesters in the capital.
"We will prosecute everyone," deputy Bangkok police chief Piya Tawichai said, adding that 74 protesters had been arrested since October 13.
Protesters seek the removal of Prime Minister Prayuth, accusing him of engineering last year's election to keep hold of power he first seized in a 2014 coup. He says the election was fair.
The protesters have also grown more vocal in demanding reforms to the monarchy to reduce the powers of King Maha Vajiralongkorn. The Royal Palace has made no comment on the protests or protesters' demands.
Protesters have said they will demonstrate every day, but had yet to set out a plan for protests on Monday.
Prayuth has said he will not quit. Speaking at Government House on Monday, Prayuth said he supported a proposal for a special parliament session to discuss the situation. His supporters have a majority in parliament.
"We are just asking people not to do wrong and destroy the government and people's property," he said. "What the government needs to do is to protect the monarchy."