Some 66 local and international human rights groups have called on the army to withdraw legal action against three human rights defenders for their report on torture.
The human rights advocates are Pornpen Khongkachonkiet, Anchana Heemmina and Somchai Homlaor.
The army has brought defamation charges against them under the Criminal Code and the Computer Crimes Act for their report on torture and ill-treatment in the far South by soldiers during 2014-2015.
The report, documenting 54 cases of inhumane treatment in detention, was published in February this year. The research and report were partly funded by the United Nations Voluntary Fund for Victims of Torture.
On June 8, Internal Security Operations Command (Isoc) Region 4 informed Ms Pornpen over the phone that Isoc 4 had sought power of attorney from the Royal Thai Army and submitted a complaint to Yala Mueang police station on May 17 about the report.
"We are gravely concerned about the legal action taken by the Royal Thai Army," the groups said in a statement Monday. "We are disturbed regarding information that authorities have already interrogated six witnesses. This legal action has been taken despite the human rights defenders' best efforts to engage authorities on the evidence of torture and ill-treatment presented in the report," they said.
"We deem the army's action to be an unreasonable, arbitrary, and a heavy-handed attempt to silence all complaints of allegations of torture against the authorities," the statement added.
According to the group, the report was sent to Lt Gen Wiwat Pathompak, of the 4th Army, on Jan 8, one month before its publication. However, military officials have dismissed the report and questioned the intentions behind it.