Concern is mounting for an Australian activist who has gone missing in Cambodia after a human rights organisation alleged he was abducted by Vietnamese authorities in an act of “transnational repression”.
Democracy campaigner Tran Hiep was expected to meet his wife, Chloe Dang, in Bangkok after travelling to Phnom Penh to meet human rights defenders.
However, the 50-year-old Melbourne man never boarded his flight and has not been heard from since September 18.
Mr Hiep, founder of the Australian Alliance to Combat Human Trafficking, had travelled with Vietnamese-Norwegian human rights activist Nguyen Duc Thuan. The pair were due to meet dissident Vietnamese activists in Cambodia for training.
Viet Tan, a pro-democracy political party representing the Vietnamese diaspora, has accused Vietnamese authorities of kidnapping the two men. It rejected claims that they had illegally crossed into Vietnam from the Cambodian border.
The advocacy group, which counts Mr Hiep and Mr Thuan among its members, said the pair had no intention of entering Vietnam. It accused Vietnamese authorities of using fabricated charges to conceal what it described as an act of “transnational repression”.
“This is a blatant fabrication intended to conceal the fact that the Viet Tan members were abducted in Cambodia and forcibly taken to Vietnam,” the group said in a statement released on Monday night.
AAP has contacted Vietnamese authorities for comment.

Tran Hiep, founder of the Australian Alliance to Combat Human Trafficking, was in Cambodia with Vietnamese-Norwegian human rights activist Nguyen Duc Thuan to meet dissident Vietnamese activists for training.
Viet Tan is urging Norwegian and Australian authorities, along with human rights organisations, to pressure the Vietnamese government to release both men immediately and unconditionally.
“Mr Thuan is diabetic and requires daily insulin injections. He must be guaranteed full access to medication and medical care,” the organisation said.
Ms Dang said she was deeply concerned about her husband’s safety.
ALSO READ: Grandparents of Missing Boy Gus Speak Out: ‘Tensions’
“My family and I are really worried about his safety, and we just only want to know where he is and what happened to him,” she told AAP at Bangkok airport before boarding a flight to Melbourne.
“My husband deserves protection, and I really hope the Australian government will continue to put pressure on Cambodia to do an investigation to find out where he is right now.”
Vietnam has intensified its crackdown on dissidents in recent years, with more than 55 activists arrested under broad criminal laws in 2025.
Civil society organisations and United Nations human rights experts have repeatedly warned that Vietnamese authorities are increasing co-operation with neighbouring governments to target advocates.
“Their disappearance is not an ordinary ‘missing person’ incident. Both men are long-time human rights advocates and Viet Tan members,” the group said.

Democracy campaigner Tran Hiep was due to meet his wife, Chloe Dang, in Bangkok after travelling to Phnom Penh to meet human rights defenders.
Ms Dang, 36, said her husband’s disappearance had taken a serious psychological toll.
“It’s been 11 days and I’m really in the dark,” she said, choking back tears. “I don’t know where he is or how he’s doing — it’s driving me crazy. Everything is really uncertain.”
The Australian government confirmed consular officials were in contact with Ms Dang but declined to comment further.
‘The Department of Foreign Affairs and Trade is providing consular assistance to the family of an Australian reported missing in Cambodia,’ a department spokesperson told AAP on Monday.
The families of the missing men have filed an appeal with the UN Working Group on Enforced or Involuntary Disappearances.