Cambodian-born Hong Lim, the member for Clarinda, who is also Victoria's Parliamentary Secretary for Asian Engagement, told Fairfax Media that barring him from returning to Cambodia is a violation of his human rights.

"It demeans the regime but we can't expect much from a government which Human Rights Watch branded as violating human rights on a daily basis," Mr Hong Lim said in an email from China, where he is preparing for a visit next month by Victorian Premier Daniel Andrews.

"My only concern is they might continue to behave like an animal, hurting my family, friends and supporters in Cambodia," he said.

Mr Hong Lim described Mr Hun Sen's government as a "beast" last week during an interview on Radio Free Asia about the recent murder in Phnom Penh of political activist Kem Ley.

Cambodia's Ministry of Foreign Affairs issued a statement slamming Mr Hong Lim's comments as "disgraceful" and said it was "very shocked to learn about the great humiliation brought upon the Cambodian nation by Mr Hong Lim".

"The humiliation made by Hong Lim upon the Cambodian nation has pushed (the ministry) to consider him as persona non grata for the Kingdom of Cambodia," it added.

The Australian embassy told the Cambodia Daily that Mr Lim did not speak for the Australian government but that "Australia has a robust tradition of different views being aired in public discussion".

Human rights groups have accused Mr Hun Sen's government of stepping up repression over the past year by jailing critics, attacking opponents and passing draconian laws to increase the ruling party's stranglehold on the country's institutions.

Former Australian foreign minister Gareth Evans in July called for the international community to put "maximum pressure" on the Cambodian government to improve the country's human rights situation, including possible sanctions on top officials.

"I think political responses from the rest of the world and certainly the rest of the region have been far too muted given the scale of the violations that have been going on for . . . a very long time now," said Professor Evans, chancellor of the Australian National University, who was the architect of the 1991 Paris Agreement that ended Cambodia's civil war.

Speaking on the Policy Forum podcast hosted by the ANU's Asia and the Pacific Policy Society, Professor Evans accused Mr Hun Sen's regime of overseeing land grabs, curtailing free speech and reacting violently to perceived threats.

He also said the murder of Mr Kem Ley had "all the hallmarks of a political assassination".

Mr Hong Lim, who is a co-convener of the Victorian Parliament's Friends of Burma, an honorary adviser to more than 20 community organisations and a former commissioner on the Ethnic Affairs Commission, told Fairfax Media that Australia should "hang its head in shame" over the $55 million deal to send refugees to Cambodia from Nauru.

"Only Hun Sen would do it – for the money," he said.

Only one refugee from Nauru is now living in Cambodia but the Turnbull government continues to spend money trying to keep the agreement from collapsing completely.

Cambodia's media has revealed that Canberra has hired a second service provider - Connect Settlement Agency - to provide services for Nauru refugees arriving in the country.

But the multi-country-supported International Organisation for Migration (IOM) has already received millions of dollars to care for refugees sent there.

The Australian government has refused to explain the need for a second agency provider for only one refugee, who is deeply unhappy and wants to leave the country.