Russian prosecutors asked a court on Monday to sentence former U.S. marine Paul Whelan, who is on trial accused of spying for the United States, to 18 years in a maximum security prison, according to his lawyer. 

Whelan, a 50-year-old U.S. national who also holds British, Canadian and Irish passports, has been in custody since he was detained in a Moscow hotel room in December 2018. He says he was set up and has pleaded not guilty to the charge.

According to his lawyer Vladimir Zherebenkov, Russian prosecutors accuse Whelan of being a ranking U.S. military intelligence colonel and say he was caught red-handed trying to obtain state secrets. Zherebenkov, on the other hand, claims his client was tricked and when he accepted a USB drive from an acquaintance, he believed it contained holiday photos, not Russian classified material.

"This was a game by Russia's Federal Security Service," said Zherebenkov.

The trial, which began on March 23, has been closed to the public as its content broaches classified information. Russian authorities also blocked journalists and embassy employees from attending recent hearings over coronavirus concerns.

At the time of his arrest, Whelan was the director of global security for auto parts supplier BorgWarner. He served in the U.S. Marine Corps for 14 years and was discharged for bad conduct in 2008. 

Whelan claims he was visiting Russia to attend a wedding at the time of the arrest. He has said that evidence he provided was ignored and that the court was biased in favor of the prosecution and security services.

During his appearances at hearings, he also alleged he had been ill-treated by prison guards and denied medical attention. Russian authorities have refuted this, accusing Whelan of faking health problems to draw attention to his case.

A verdict in the trial is expected on June 15.

"If the situation does not get politicized, if the sentence is determined in an objective, fair way, there should be an acquittal as the defense asked for," Zherebenkov said.

U.S. authorities have called the charges against Whelan "spurious" and have called on Russia to release him, describing the case as a "significant obstacle" to improving bilateral ties.

U.S. Ambassador in Moscow John Sullivan slammed the proceedings, saying they amounted to a "secret trial" and a "mockery of justice".

"There is no legitimacy to a procedure that is hidden behind closed doors. It is not transparent, it is not fair, and it is not impartial," he said.

(With input from AFP, Reuters)