The defence team for Nuon Chea has called for senior government and military figures – including Prime Minister Hun Sen – to appear before the Khmer Rouge tribunal.

In a submission made public on Monday, the defence argued that delving into the extent of a “treasonous rebellion” backed by Vietnam was crucial to ensure their client, the Khmer Rouge’s brother number two, was given a fair trial.

The defence requested the court summons 35 witnesses – four of them top-ranking government leaders, and three from the armed forces, as well as filmmaker Robert Lemkin.

“Deciding not to summons the requested witnesses will effectively and finally prevent Nuon Chea from presenting his defence altogether,” the filing read. “This will constitute a straightforward violation of . . . Nuon Chea’s right to a fair trial.”

Chea’s international lawyer, Victor Koppe, said the matter was not just about calling high-profile witnesses, but was also the defence’s “final chance” to present its case to the public.

“We haven’t been able to do anything in the last nine years . . . we were never allowed to do our own investigation – that was strictly forbidden,” he said.

The submission stated: “Following its 1978 invasion, Vietnam occupied Cambodia for a decade [and] installed a loyal puppet government that is still effectively in power today.”

Koppe said that he was “pessimistic” the witnesses would be called, and doubted high-profile ones would appear if summonsed.

“They are afraid that we will expose their role,” Koppe said, alluding to the crushing of a Cham rebellion and the forced evacuation of Phnom Penh, in which the defence says current National Assembly President Heng Samrin played a part.

When asked if the submission politicised the trial, Koppe responded: “This trial is 100 per cent political to start with . . . it’s impossible not to get political.”

Government spokesperson Phay Siphan said parliamentarians had immunity to not appear before the court.

He added that the court should focus its attention on why the regime executed almost 2 million of its own people. “It’s a strategy by the defence to raise the issue of the Vietnamese as a scapegoat to deviate the focus of the [tribunal],” Siphan said.

Trial observer Heather Ryan described the filing as “an extended critique of the trial”.

“The court has the difficult task of evaluating the relevance of the requested witnesses without being influenced by any of political pressure that has influenced past decisions not to summon witnesses with political influence or connections,” she said via email.