Three international human rights organisations have demanded a probe into allegations that a female red-shirt activist was tortured during her detention by the National Council for Peace and Order (NCPO) last month.
The Office of the United Nations High Commissioner for Human Rights (OHCHR), Human Rights Watch (HRW) and the International Commission of Jurists said authorities should immediately investigate Kritsuda Khunasen's claims she was tortured during her 29-day detention with the military.
HRW says Ms Kritsuda, 27, was secretly detained without charge at a military camp from May 27 until June 24, 2014.
Ms Kritsuda appeared in a YouTube video over the weekend alleging the military tortured and assaulted her as it tried to make her implicate deposed prime minister Thaksin Shinawatra in firearms offences.
She said that soldiers beat her during interrogation and covered her head in a plastic bag until she lost consciousness.
She reportedly left Thailand before releasing the video and is said to be seeking political asylum in Europe.
The NCPO has denied the allegations, saying she was making up the charges to support her asylum request. They said it does not make sense that the military should torture her and then set her free.
Ravina Shamdasani, OHCHR spokeswoman, said the Geneva-based UN agency was concerned about the arrest and detention of politicians, activists, academics and journalists following the coup.
She said more than 700 individuals have been summoned and arrested by the NCPO and while most of them were released within a week, some were detained for more than seven days without access to lawyers and their families.
"We have grown concerned that incommunicado detention creates an environment for possible human rights abuses, including torture and ill-treatment," Ms Ravina said.
Brad Adams, Asia director at HRW, said the Thai junta's response to Ms Kritsuda's allegations has been dismissive, raising broader concerns for authorities' treatment of all detainees.