Viet Tan alleges Australian and Norwegian-Vietnamese activists abducted by Vietnamese authorities in Cambodia

Pro-democracy group Viet Tan alleges a Melbourne man and his Norwegian Vietnamese colleague, who went missing in Cambodia more than a week ago, were abducted by Vietnamese authorities and forcibly taken to Vietnam, in what it calls an act of transnational repression.

Hiep Tran, 50, and his colleague Duc Thuan Nguyen, 52, have not been heard from since the morning of September 18.

The pair had travelled to Phnom Penh to meet Vietnamese human rights activists.

They flew into the Cambodian capital from Bangkok on September 15, and were in regular contact with their families until September 18.

They did not board their return flight to Bangkok at 10:30am the next day.

Overnight, Vietnamese state media reported the men had been detained, according to Viet Tan, the group both men belong to and which the Vietnamese government considers a terrorist organisation.

Viet Tan said authorities alleged the pair "illegally entered Vietnam from the Cambodian border".

But the group rejects that account, saying the men had no intention of entering Vietnam and were abducted in Cambodia, then forcibly taken across the border.

The ABC has not seen the state media report but has contacted Vietnamese authorities for comment.

'A blatant fabrication'

In a statement, Viet Tan said the claim was a fabrication intended to cover up an abduction that violated Cambodia's sovereignty and international law.

The group said the men were travelling to the Kaoh Andaet area of Cambodia when they went missing.

Viet Tan has called on the Australian and Norwegian governments to urgently request direct access to the men to confirm their condition and safety.

It said Mr Nguyen was diabetic and required daily insulin injections, and must be guaranteed access to medication and medical care.

It has also urged both governments and international human rights organisations to pressure the Vietnamese government for the men's immediate and unconditional release.

Family's fears

Speaking before news of her husband's detention, Mr Tran's wife, Chloe Dang, said the couple travelled to Thailand for a holiday before her husband made a side trip to Cambodia.

She said he was a passionate human rights activist but that she feared the men were targeted, or kidnapped, because of their advocacy.

Ms Dang was waiting at Bangkok airport when the pair failed to appear, and was told Mr Tran had never boarded the flight.

"Our last conversation was him checking in on me in Bangkok, making sure I was safe and OK. He always checks in with me," she said.

She said she had lodged a missing person's report in Cambodia, and was liaising with Australian consular officials, but was worried not enough was being done.

A spokesperson for DFAT said it was providing consular assistance to the family of an Australian reported missing in Cambodia, but could not comment further due to privacy obligations.

'Not a normal tourist disappearing'

Phong Nguyen, who represents the group in Australia, said Mr Tran was a long-time advocate who trained activists in digital security.

He previously worked in IT for a large bank and for Telstra, but had left to focus on human rights work.

Mr Nguyen said the men had been supporting human rights activists for more than 20 years and were meeting activists who were not Viet Tan members.

"What's concerning is that this is not a normal tourist disappearing while travelling," Mr Nguyen said.

Rights groups including Human Rights Watch and Amnesty International have documented the jailing of Vietnamese citizens for online posts and activism.

Mr Nguyen said sentences of 15 or 20 years were not unusual, and that ordinary people were at risk, not only high-profile figures.

He also pointed to a rise in transnational repression, where governments targeted critics abroad, claiming there had been a significant increase in the past year in overseas Vietnamese nationals being "captured, kidnapped" and sentenced.

Mr Nguyen pointed to Australian citizen Chau Van Kham, a Viet Tan member who spent four and a half years in prison in Vietnam after his arrest in 2019.

Mr Nguyen said Mr Tran and Mr Thuan understood the dangers of their work, which made their silence even more alarming.

"Something must have happened very quickly that they couldn't alert," he said.