The Cambodian military will not investigate how an Australian was killed on a shooting range last week, after allegedly trying to "cover up" the nature of the incident.

Key points: The incident is not an official case, Cambodia's Defence Ministry spokesman says

The incident is not an official case, Cambodia's Defence Ministry spokesman says Hun Sen reportedly offered his condolences to Mr Turnbull, but it was unconfirmed by the PM's office

Hun Sen reportedly offered his condolences to Mr Turnbull, but it was unconfirmed by the PM's office China and Cambodia began a joint military exercise in the Kampong Speu province

The Phnom Penh Post newspaper quoted Defence Ministry spokesman Chhum Socheat as saying there would be no investigation as it was a "private case".

"Inside the unit, they are good friends with [the Australians]. They allowed them to visit privately," he told the Post.

"It's not an official case, and is not concerned with the military operation."

An Australian and a Cambodian were killed in an explosion at a shooting range on a tank base in Kampong Speu province, which operated as a money-making activity for tourists.

Three other men were injured, including another Australian.

Sorry, this video has expired A man, not a victim in the explosion, fires a weapon at the shooting range in Cambodia.

Initially, Cambodian authorities said the foreigners were "military trainers", but Australia's Department of Defence later confirmed they were not ADF personnel and were not involved in any official training.

A source described the Cambodian Government's first response as a "cover-up".

The names of the Australians given to police at the scene — Aarou Sweeibo and Bra Davey — appear to be mistranslated or made up.

Cambodia's authoritarian slide discussed at ASEAN summit

Hun Sen threatened to "beat" protesters who burned his effigy in Sydney. ( Reuters: Samrang Pring )

The Phnom Penh Post quoted Kampong Speu Governor Vy Samnang as saying that Prime Minister Hun Sen had offered his condolences to Malcolm Turnbull in Sydney on Friday morning, where both were attending the ASEAN summit.

However, the Prime Minister's office declined to confirm that Hun Sen offered condolences.

"We do not comment on the detail of the conversations between leaders," a media adviser at the Department of the Prime Minister and Cabinet told the ABC.

In a separate statement, the Department of Foreign Affairs and Trade (DFAT) said Cambodia's authoritarian slide had been discussed at the ASEAN summit.

"Australia remains deeply concerned by the narrowing of democratic space in Cambodia," a DFAT spokesperson said.

"We've made our views clear to the Cambodia Government through direct and regular representations, including at the ASEAN-Australia Special Summit in Sydney."

Hun Sen threatened to "beat" protesters who burned his effigy in Sydney, but several hundred members of the Cambodian-Australian community turned out to peacefully demonstrate.

Cambodia and China begin drills

China and Cambodia's war games come a year after Cambodia abruptly cancelled a planned joint exercise with Australia. ( ADF, file photo )

Just days after the deadly explosion on the Armoured Headquarters base in Kampong Speu, China and Cambodia began a joint military exercise in the province.

The pro-government Khmer Times newspaper reported that 600 Cambodian soldiers and 200 Chinese troops will fire 18,000 rounds of various ammunition during Golden Dragon 2018.

The war games come a year after Cambodia delivered a "slap" to Australia, abruptly cancelling a planned joint exercise called Dawn Kouprey, saying it was too busy preparing for elections.

Military exercises with the United States were also cancelled, part of Cambodia's wider shift of allegiance towards China.

For Cambodia, China does indeed represent a "golden dragon".

Beijing has offered billions of dollars worth of grants and soft loans to Hun Sen, with none of the criticisms about human rights and democracy attached to "Western" aid.

In return, Cambodia has done China's bidding with ASEAN, especially on the issue of the disputed South China Sea.

Beijing's financial and political backing has emboldened Hun Sen to cast off any pretence of democracy, with the opposition party dissolved and its leader jailed in preparation for an election in July.