Thailand faces growing international pressure, including from US President Donald Trump's new secretary of state, to avoid deporting a group of Uyghurs to China.
Some 48 members of the persecuted ethnic group have been detained by Thai authorities since 2014, when they were arrested among hundreds of others trying to cross the Thai border to seek asylum.
"We are concerned they are at risk of suffering irreparable harm," United Nations experts, including the special rapporteur on torture, said in a statement on Wednesday.
"The treatment of the Uyghur minority in China is well-documented."
The Uyghurs are a mostly Muslim, Turkic ethnic group, whose culture and language are distinct from China's ethnic Han majority.
Since 2017, Chinese authorities have waged what they call a "people's war on terror" aimed at stamping out alleged extremism among Uyghurs.
At least 1 million Uyghurs and other Muslim ethnic minorities are estimated to have been detained extrajudicially in detention camps, which Beijing says are vocational training centres.
According to the UN human rights experts, 23 out of the 48 detainees in Thailand "suffer from serious health conditions, including diabetes, kidney dysfunction, paralysis of the lower body, skin diseases, gastrointestinal illnesses, and heart and lung conditions".
The detainees issued a public letter earlier this month to raise the alarm over their imminent deportation, which was reportedly planned to coincide with the 50th anniversary of diplomatic relations between Bangkok and Beijing.
"We could be imprisoned, and we might even lose our lives," the letter said.
"We urgently appeal to all international organisations and countries concerned with human rights to intervene immediately to save us from this tragic fate before it is too late."
A spokesperson for the Chinese embassy in Bangkok said in a statement that the Uyghur detainees were terrorists, declaring Western media coverage of their situation "unfounded and irresponsible".
Washington joins human rights groups in calling for halted deportations
US Secretary of State Marco Rubio, who was sworn in on Tuesday last week, told his confirmation hearing in the US Senate that he would pressure Bangkok not to follow through with the deportations.
Mr Rubio said it was an opportunity to "remind the world" about the group's persecution in China, which he called "one of the most horrifying things that has ever happened".
"Thailand is a very strong US partner, a strong historical ally," he said.
"I think diplomacy could really achieve results because of how important that relationship is and how close it is."
Mr Rubio, a Republican senator from Florida, is one of the leading US critics of Beijing and has long championed the rights of Uyghurs.
On his first day as secretary of state, Mr Rubio met with Foreign Minister Penny Wong and their Japanese and Indian counterparts as part of the Quad foreign leaders meeting — a grouping China argues is reviving Cold War tensions.
Speaking in Washington, Senator Wong said the meeting was "a demonstration of the collective commitment of all countries to the Quad, an iron-clad commitment in this time where close cooperation in the Indo-Pacific is so important".
Thailand has a track record of forcibly returning asylum seekers to their country of origin, including deporting 100 Uyghurs to China in 2015.
Some returnees are known to have been given prison sentences after returning to China, while Uyghur groups say many have simply vanished.
Five Uyghur detainees including two children have died in Thai detention over the past 11 years, according to the UN.
"Successive Thai governments have kept the Uyghurs in inhumane detention, while under pressure from the Chinese government to send them to China," said Elaine Pearson, Asia director at Human Rights Watch.
"The current administration of Thai Prime Minister Paetongtarn Shinawatra can end this abusive cycle by immediately releasing the detained Uyghurs and allowing them to travel to a safe third country."
The ABC has approached Thailand's embassy in Canberra for comment.
