Moscow, April 14 (TIWN) The trial of a former US marine accused of spying has begun behind closed doors in Moscow, 16 months after his arrest, a media report said.

The Russian government has said that Paul Whelan was caught "red-handed" with state secrets, the BBC reported on monday.

The American could be facing up to 20 years in prison.

FSB security officers burst into Paul Whelan''s room at a central Moscow hotel in December 2018.

He was detained with a USB flash drive which the FSB has said that contained secret information.

Whelan, who has visited Russia many times, had previously told the BBC that an old friend had turned up at his room uninvited and planted the drive.

"It''s a case without any proof in over 16 months... That''s intolerable," US Ambassador John Sullivan told the BBC.

He called Whelan''s treatment, including the lack of proper medical care for a pre-existing health condition, "vile" and "inhumane".

"He hasn''t been able to speak to family or friends in 16 months," Ambassador Sullivan told the BBC.

"It''s really shameful."

The diplomat was not permitted into court to speak to Whelan, due to extra restrictions during the coronavirus pandemic.

Prison visits have also been suspended because of the outbreak.

In court on Monday, Whelan''s state-appointed lawyer Vladimir Zherebenkov called the case a "provocation" and "fabrication" by an intelligence officer looking to advance his career.