Rights activists have warned that two Uyghur men held in Thailand could face grave danger if they are deported to China, with one of the men saying he would be treated "like a slave" if forced to return.

The case comes a year after Thai authorities forcibly sent 40 Uyghur men back to China, despite appeals from the men themselves and the United Nations. The United States and Canada had reportedly offered to resettle that group, but Bangkok appeared unwilling to anger Beijing. The UN says the whereabouts of those returnees are still unknown.

Human rights groups say the two men now at risk were recently moved to an immigration detention centre, raising fears that Thai authorities may once again yield to pressure from Beijing. Elaine Pearson, Asia director at Human Rights Watch, urged that the men be allowed to travel to a safe third country. "Previous Thai governments have kept Uyghurs in inhumane detention for years and then complied with Beijing's demands to send them to China, where they were forcibly disappeared," she said.

The pair had been serving seven-year prison sentences for offences linked to an attempted escape from immigration detention in January 2020. They were among more than 200 Uyghur men, women and children detained by Thai police in 2014 near the Malaysian border after fleeing China. Women and children from that group have since been released to Turkey, while the men have been deported to China in separate batches, drawing criticism from the United Nations and the US secretary of state, Marco Rubio.

Uyghurs, a largely Muslim Turkic minority mainly from China's Xinjiang region, have faced decades of repressive and discriminatory treatment, including the mass incarceration of hundreds of thousands of people in detention camps that critics say aim to erase their cultural identity. The UN has condemned Beijing's crackdown as a potential crime against humanity. China defends its Xinjiang policies as measures for poverty alleviation and counter-terrorism.

The girlfriend of one of the men, Marzeyya Kasem, who asked to be identified by her Islamic alias, shared a letter he wrote to her in July with a Thai rights group. In it, he said he would be "like a slave" if sent back. "Sometimes I thought why I'm a human being. What I do wrong against China … no want to go back to China," he wrote. She said her boyfriend, whose name is being withheld for security reasons, told the Guardian he wanted to go "anywhere else but China".

The two men reportedly appealed their case to Thailand's office of the National Human Rights Commission on Wednesday. Relatives of Uyghurs have said the Chinese government was "paranoid about Uyghurs going to a safe country in large numbers and living together", and preferred to see them deported.

It remains unclear whether Beijing has filed a formal extradition request. Thailand's national security council chief, Chaipruak Doungprapat, told reporters that the two men, along with three other Uyghurs still in prison, had outstanding arrest warrants in China. The credibility of such warrants has been questioned, since at least one of the men, Kasem's boyfriend, was a minor when he left China. "If they are really wanted for a crime in China, why didn't China immediately issue a [Interpol] red notice [when they were detained in 2014]?" Kasem asked, adding that she believes Bangkok is trying to build a more convincing legal basis for deportation after the criticism it received last year.

A spokesperson for China's foreign affairs ministry said: "The cooperation between China and Thailand in combating cross-border illegal and criminal activities such as smuggling is consistent with the laws of the two countries, international law and international practice." A spokesperson for Thailand's foreign affairs ministry declined to comment.