Moscow City Court found Whelan guilty of receiving classified information as he stood in the dock with a sign that read "Sham trial!" and pleaded for US President Donald Trump to intervene in the case.

The court process is "slimy, greasy Russian politics nothing more, nothing less," he said.

Whelan, 50, has been held in a Moscow jail since his arrest in December 2018 and his trial was held behind closed doors because of the accusations of seeking to obtain state secrets.

Throughout the trial he maintained his innocence, saying he was framed and comparing himself to the hapless comedy character Mr Bean.

"Russia thought they caught James Bond on a spy mission, in reality they abducted Mr Bean on holiday," he said.

Whelan says he was detained on a visit to Moscow to attend a wedding when he took a USB drive from an acquaintance thinking it contained holiday photographs.

The prosecution had asked the judge to sentence Whelan to 18 years in a strict-regime penal colony, just short of the 20 years maximum term for the charge.

- 'No evidence' -

The US ambassador to Moscow John Sullivan condemned the trial as unfair and lacking transparency.

"I am disappointed, outraged by what I just heard," he told reporters in court.

"(Whelan has) been sentenced to 16 years in prison with no evidence that's been produced.

"I can't say I'm surprised. This is the direction this case has been heading from the beginning," he added.

The prosecutor summed up last month by saying Whelan tried to receive information that was a state secret and could harm Russia's security, Whelan's lawyer Vladimir Zherebenkov told reporters.

The prosecutor claimed that Whelan has the rank of an officer -- "at least a colonel" -- at the US defence intelligence agency, the lawyer said.

Whelan's family had said ahead of the verdict that a guilty verdict was a foregone conclusion.

After Monday's ruling, his brother David said in a statement that he family would continue to fight for his release, and criticised the court's politically motivated verdict.

"We had hoped that the court might show some independence but, in the end, Russian judges are political, not legal, entities," he said.

Whelan was dishonourably discharged as a marine before working as head of global security at a US auto parts company.

There had been suggestions that Whelan -- who also has British, Canadian and Irish passports -- could be returned to the US in a prisoner swap.

Whelan's lawyer said on Monday that Russian intelligence services were considering an exchange with two Russians detained in the United States, including pilot Konstantin Yaroshenko, imprisoned on drug smuggling charges.

David Whelan, the brother, said recently that the family hoped a conviction would allow Russia and the United States to "begin discussing Paul's release immediately".

Whelan had complained of being mistreated in prison and late last month underwent an operation in a Moscow hospital that his family said was emergency hernia surgery.

The US embassy criticised the Russian authorities for waiting until his condition was "life-threatening to provide him medical attention", while the Russian foreign ministry described the procedure as "simple".