The Australian government has chartered a plane to move the first group of refugees from Nauru to Cambodia within days as part of a $40m resettlement deal, sources on the island have said.

Guardian Australia has seen several letters that were reportedly distributed by Australian immigration staff to refugees on Nauru and a spokesman for the International Organisation for Migration has confirmed it is sending an official to Nauru.

“We will send an official to Nauru in the coming days with the expectation of possible movements but don’t have any further information for the moment,” he said.

The letters handed out to refugees offer them an opportunity to settle in Cambodia, where they will be eligible for citizenship in seven years.

“The opportunity to settle in Cambodia is now available to you. The first flight from Nauru to Cambodia for refugees will be as soon as 20 April 2015. Moving to Cambodia provides an opportunity for you and your family to start a new life in a safe country, free from persecution and violence, and build your future,” the letter says.

“Cambodia is a diverse country with multiple nationalities, cultures and religions. They enjoy all the freedoms of a democratic society including freedom of religion and freedom of speech.”

It goes on: “Cambodia is a safe country, where police maintain law and order. It does not have problems with violent crime or stray dogs.”

The letter says the refugees will be able to send their children to school in Cambodia, and will be given support including cash and a bank account, assistance finding work, income support, language training and health insurance.

One refugee living in the community on Nauru who received the letter told Guardian Australia: “The letter was very confusing because it didn’t mention anything exactly. They said support but the people don’t know what exactly they mean by support.”

“People Googled Cambodia and they said it’s not a developed country, there is lots of dangers, and I know people have lots of concerns about it. So not many people are interested.”

The letter says they will be offered temporary accommodation in Phnom Penh in the “style of a serviced apartment, guest house or villa”. After six to eight weeks, case managers will assist them in gaining access to further accommodation, the letter says.

Healthcare in Cambodia “is of a good quality for the region, with many doctors and hospitals that treat both Cambodians and foreigners”, it says.

It is unclear how many refugees have accepted the offer. Guardian Australia is aware of at least one family confirmed on the flight manifest.

Numerous aid groups have warned the Australian government that Cambodia is ill-equipped to take on refugees because it has a poor human rights record and widespread poverty.

Critics of the deal, including human rights groups in Cambodia, argue the developing nation is poorly suited to accept and support refugees. Cambodia remains one of the most deeply corrupt nations on earth (156th on the Transparency International list of 175 countries) and has, according to Human Rights Watch, “a terrible record for protecting refugees and is mired in serious human rights abuses”.

The Australian director of Human Rights Watch, Elaine Pearson, said Cambodia was “far from a tropical democratic paradise.”

“The reality is that Cambodia is a struggling economy with ineffective and corrupt law enforcement where its own citizens face corruption, repression and violence on a daily basis.

“Basic freedoms are not protected at all in Cambodia – those who speak out against the government risk jail - at least nine women were jailed last year for protesting about flooding in their area. Far from maintaining law and order, too often police are implicated in abuses such as torture, excessive use of force and petty corruption.

“And as for no stray dogs, well that seems to be a sick joke. The UN human rights office has reported how dogs have been used to hunt down Vietnamese asylum seekers in the forest in Ratanakiri province in recent months.”

In March, Australia signed a new memorandum of understanding with Cambodia following a visit from the immigration minister, Peter Dutton.

The immigration department has been contacted for comment.