As the ever-controversial Australia-Cambodia refugee deal turned three yesterday, it came under fresh scrutiny thanks to the impending deportation of Montagnard refugees and Cambodia’s downward political spiral.

The A$55 million deal, inked on September 26, 2014, to the clinking of champagne glasses, has seen just seven refugees from the island detention centre of Nauru move to Cambodia. Of those, four have since returned to their home countries. The three who remain – a Rohingya Muslim and two Syrian men – can’t go home.

Syria continues to be savaged by war, while over the past month, some 400,000 Rohingyas have fled across Myanmar’s border into Bangladesh – an exodus human rights experts say was prompted by widespread violence and a campaign of ethnic cleansing.

While all eyes are on the crisis enveloping Rakhine state, Cambodia has quietly rejected refugee status for 29 Montagnards – a decision the United Nations refugee body (UNHCR) called a “grave error in judgment” given the strength of their claims and the documented risks of their return to Vietnam.

The UNHCR has offered to take the 29 – along with seven who have been recognised by Cambodia as refugees – to the Philippines and on to a third country for resettlement. That offer has so far gone unheeded by Cambodian officials, who maintain they are fulfilling their obligations under the Refugee Convention and have “no right” to send the would-be refugees anywhere but Vietnam.

The impending deportation was heralded earlier this month, when rejected refugees were given 15 days to leave the country. That deadline lapsed last Friday, with the Montagnards – a Christian minority group hailing from Vietnam’s Central Highlands – anxiously awaiting their fate with each passing day.

Read more: Montagnards returning to Vietnam speak of dread for what awaits them

Refugee advocates are now saying Cambodia’s actions reveal a failure to uphold the Refugee Convention. Asia Pacific Refugee Rights Network programme coordinator Evan Jones last week said Australia – which cemented its agreement on the premise that Cambodia would be a safe haven for unwanted refugees stranded on Nauru after trying to reach Australia by boat – had an “ethical obligation” to intervene.

“Such action by the Cambodian Government would be tantamount to refoulement and in flagrant disregard of the 1951 Refugee Convention,” he said in a statement.

“This action by Phnom Penh seriously calls into question Australia’s claim that Cambodia is a safe country and one that would be welcoming to refugees currently detained on Nauru.”

“The Australian dilemma would be selling a lie of Cambodia as a fair country if it didn’t intervene,” he added in an interview yesterday, noting such intervention could involve restricting aid or an ambassadorial appeal to Interior Minister Sar Kheng.

Cambodian Refugee Department officials did not respond to calls yesterday. Interior Ministry spokesman Khieu Sopheak, meanwhile, said Cambodia needed to balance its Refugee Convention obligations with domestic immigration law – which required the deportation of illegal immigrants – and insisted the Kingdom didn’t need to be lectured on refugee status, before hanging up.

Paul Power, CEO at the non-profit Refugee Council of Australia, said Australia “must act” when “Cambodia’s adherence to the Refugee Convention is clearly under threat”.

The “forced return” of the Montagnards, Power said, “would not only undermine Cambodia’s reputation for respecting international law but would inflict further damage on Australia’s credibility on refugee protection”.

That credibility is already under strain. Reports of abuse are rife in the detention centres of Nauru and Manus islands, prompting a court case and a A$70 million government payout to Manus refugees due to physical and psychological injury inflicted under their detention conditions.

Australia has outsourced its obligations, first to Cambodia and now to the US, which has agreed to take an initial 54 refugees of more than 1,000 awaiting resettlement. The Guardian last week reported Australia was offering A$25,000 to Rohingya refugees to return to Myanmar.

Australia’s Department of Immigration and Border Protection was unable to respond to emailed questions yesterday.

Meanwhile, instead of provoking a response or intervention in the case of Cambodia’s failings, Australia’s refugee deal could instead have a silencing effect.

Paul Chambers, from the College of Asean Community Studies at Naresuan University in Thailand, said the refugees in both countries have been used as pawns for political ends. The Australia-Cambodia deal’s sole aim was to keep politically “undesirable” refugees off Australian shores, while the Montangards in Cambodia are caught between Phnom Penh and its one-time patron and close ally, Hanoi.

Their situation recalls Uighur asylum seekers in Cambodia unceremoniously sent back to China, the Kingdom’s staunchest backer. However, the “superficial or false ethics” of both countries in signing the deal all but ensures Australia remains silent over the fate of the Montagnards, Chambers continued.

“Australia should speak out against Cambodia but that is doubtful because Canberra does not want to upset Phnom Penh’s policy of helping Canberra remove its undesired migrants,” he said.

Phil Robertson, of Human Rights Watch, said the “lack of real commitment” to protecting refugees in the region was “truly appalling”.

“What’s striking is how the governments seem to be all about either getting rid of refugees or stopping their own people from fleeing to become refugees, while completely ignoring the need to end the persecution that causes people to flee in the first place,” he said in an email.

He said Australia had invested “serious political capital” in Cambodia as a destination for refugees, and warned that if the Montagnards are sent back into harm’s way, “Cambodia’s reputation as a refugee rights respecting state will be totally destroyed and Australia will become a laughing stock in the region for believing anything different was ever possible”.

Southeast Asia expert at the University of New South Wales Carl Thayer said Australia should shut down the Cambodia resettlement deal “without delay”.

“Cambodia’s descent into dictatorship and autocratic rule completely undermines any understanding that the Hun Sen regime will provide the necessary credentials for permanent settlement with a path to citizenship and opportunities for meaningful employment to former residents of the Nauru,” he said in an email.

He said Australia should protest the involuntary return of asylum seekers – “silence is only acquiescence” – but warned the move could have implications.

“There is nothing to stop the Cambodian government from repatriating Syrians or Rohingya asylum seekers from Nauru back to their country of origin if it suits the Government,” he said. “Why should the Hun Sen regime provide assurances to asylum seekers while at the same time it is undermining rule of law domestically?”

“Cambodia’s dependence on China means that Hun Sen feels impervious to outside criticism. In this sense Hun Sen is right, Australia has little leverage.”