Lawyers on both sides are scheduled to make their closing arguments, and the prosecutors are to make their sentencing request.

Whelan, 50, who also holds Irish, Canadian and British citizenship, was detained in Moscow in December 2018 for allegedly receiving state secrets.

He maintains he visited Russia to attend a wedding and was framed when he took a USB drive from an acquaintance thinking it contained holiday photos. He faces up to 20 years in prison if convicted of spying.

"In a just system, the court would acquit Paul based on the lack of evidence," Whelan's brother David said in a statement ahead of the hearing.

"But we expect a wrongful conviction and can only hope that the sentence is at the lighter end of the range."

The trial, which began in March this year, has continued behind closed doors in a Moscow courtroom despite the coronavirus pandemic and diplomatic protests.

The US has condemned Whelan's detention saying there was insufficient evidence to hold him.

US Ambassador to Russia John Sullivan criticised Whelan's treatment in detention last month, saying it was "intolerable" that the former marine was being barred access to medical care and has not been allowed to speak to family.

Whelan, who was head of global security of a US auto-parts supplier at the time of his arrest, last year asked for the prosecutor and judge to be removed from the case.

- Hopes of spy swap -

He claimed that evidence he provided was ignored and the court was biased in favour of the prosecution and security services.

He used earlier court hearings to appeal to journalists and US President Donald Trump, and claimed he was being mistreated, not given full translations of documents and rarely granted access to his lawyer.

Yet speaking after a hearing last week, Whelan's lawyer, Vladimir Zherebenkov, said the court had been "impartial" during hearings and there had been "no violations" of Whelan's rights.

Russian authorities have barred journalists and embassy employees from attending recent hearings because of the coronavirus epidemic.

Zherebenkov said three defence witnesses failed to show up to a hearing last week over coronavirus fears, saying they did not want to play "Russian roulette" and risk their lives by attending.

Whelan's case has raised speculation that the United States and Russia could be positioning themselves for a prisoner swap, possibly involving Russian pilot Konstantin Yaroshenko, imprisoned in the United States on drug smuggling charges.

Hopes for Whelan's release in exchange for Maria Butina -- a Russian woman arrested in the US in 2018 on espionage charges -- were quashed after Butina was flown to Moscow in October last year.

The case has exacerbated underlying tensions between the US and Russia, which are at odds over the Kremlin's support for the Syrian government and separatists in eastern Ukraine.