The trio were set to appear in court on Tuesday, their editor added, urging Thai authorities not to repatriate them to the coup-hit country.
Myanmar has been in turmoil since the military ousted civilian leader Aung San Suu Kyi on February 1, triggering a mass uprising as large swathes of the population take to the streets to demand democracy.
The junta has responded with force—shooting protesters, arresting suspected dissidents in night raids, and targeting journalists and news outlets by shutting them down.
"They were arrested during a random search by the police and charged for illegal entry in Thailand," said a Monday statement by Aye Chan Naing, chief editor of Democratic Voice of Burma (DVB), which had its broadcast licence revoked in March, sending its journalists into hiding.
"DVB strongly urges the Thai authorities to not deport them back to Burma, as their life will be in serious danger if they were to return," said the Oslo-based editor, referring to Myanmar by its old name.
He told AFP the group was set to appear in court Tuesday.
Thai authorities on Tuesday confirmed the arrests but did not say if they were journalists.
DVB confirmed in a statement late Monday night that three of its journalists—along with two Myanmar activists—had escaped to neighbouring Thailand and were arrested by authorities Sunday in the northern city of Chiang Mai.
A well-known news organisation within Myanmar, DVB started as an exile media outlet during the previous junta, broadcasting uncensored reports on TV and radio.
It moved into Myanmar in 2012, a year after the military dictatorship loosened its grip.
Despite losing its broadcast licence in March, it has continued to report, posting regular updates on its Facebook page about the daily protests and crackdowns across the country.
It also broadcasts via satellite television — a move that the junta attempted to halt when it banned homes from having satellite dishes.
The Foreign Correspondents' Club of Thailand said in a statement Tuesday that if the arrested Myanmar nationals were deported, they would face "certain arrest and persecution, if not worse".
"The world is watching what the Thai authorities do in this important case for press freedom in Myanmar and the region," it said.
More than 70 journalists have been detained since the February 1 coup, according to a local monitoring group—which has tracked a total of nearly 5,000 arrests nationwide.
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