Myanmar has been in turmoil since 2021, when the military ousted the elected government led by Nobel laureate Aung San Suu Kyi, sparking a wave of anti-junta protests that have morphed into a nationwide civil war.
Myanmar's Chin state Human Rights Organisation (CHRO) last month filed a complaint with the justice department of East Timor, also known as Timor-Leste, alleging that the Myanmar junta had carried out war crimes and crimes against humanity since the 2021 coup.
In January, CHRO officials also met East Timor President Jose Ramos-Horta, who last year led the tiny Catholic nation's accession into the Association of Southeast Asian Nations (ASEAN), of which Myanmar is also a member.
CHRO filed the complaint in East Timor because it was seeking an ASEAN member with an independent judiciary as well as a country that would be sympathetic to the suffering of Chin State's majority Christian population, the group's Executive Director Salai Za Uk said.
"Such unconstructive engagement by a Head of State of one ASEAN Member State with an unlawful organisation opposing another ASEAN Member State is totally unacceptable," the state-run Global New Light of Myanmar quoted the foreign ministry as saying on Monday.
A spokesman for the Myanmar junta did not respond to calls seeking comment.
In early February, CHRO said East Timor's judicial authorities had opened legal proceedings against the Myanmar junta, including its chief Min Aung Hlaing, following the complaint filed by the rights group.
Myanmar's foreign ministry said East Timor's acceptance of the case and the country's appointment of a prosecutor to look into it resulted in "setting an unprecedented practice, negative interpretation and escalation of (public) resentments."
East Timor's embassy in Myanmar did not immediately respond to a request for comment sent via email.
The diplomatic spat comes as the Myanmar military faces international scrutiny for its role in an alleged genocide against the minority Muslim Rohingya in a case being heard at the International Court of Justice.
Myanmar has denied the charge.
