Mattohti Mattursun was one of 350 Uighur refugees, including children, who were detained in March 2014.

Mattohti Mattursun died of suspected liver failure in the Suan Phlu Immigration Detention Centre in Bangkok on April 21, according to an April 24 statement from the World Uyghur Congress and the Uyghur Human Rights Project (UHRP). He was 40 years old.

Mattohti, who was also known as Muhammad Tursun, was one of 350 Uighurs, including children, who were detained as they headed towards Malaysia in the hope of making it to safety in a third country in March 2014. The following year, at least 170 of them were transferred to Turkey while more than 100 were sent back to China, which the United Nations has said may have committed potential “crimes against humanity” in its mass internment of mostly Muslim Uighurs.

“How many more deaths will take place before Thai authorities act with humanity to release these innocent people who are merely seeking safe haven,” UHRP Executive Director Omer Kanat said in the statement. “Uyghurs around the world are filled with anguish that these refugees have been left in misery for nine years and the world has not lifted a finger to rescue them.”

World Uyghur Congress President Dolkun Isa said there were concerns about the “harsh conditions of detention, which we fear can only lead to the death of all remaining detainees”.

Like many countries in Southeast Asia, Thailand is not a party to the 1951 UN Refugee Convention, leaving asylum seekers vulnerable to arrest and detention as “illegal migrants“.

The Uighur groups’ said Mattohti was sent to hospital last Friday after weeks of severe stomach pain and vomiting as well as developing jaundice. He died shortly after he was admitted.

Thailand has yet to officially confirm his death.

In February, 49-year-old Aziz Abdullah died of pneumonia after also spending nine years in detention.

“Thai authorities are putting people at risk by keeping them for years in awful conditions in immigration detention centers,” Human Rights Watch’s Asia Director Elaine Pearson said in a statement.

“Mattohti Mattursun’s death should sound the alarm to end this abusive policy of incarcerating asylum seekers and refugees for prolonged periods.”