Paul Whelan has been held under arrest in Russia since late December and is accused of being caught red-handed "carrying out an act of espionage".

But during an appeal hearing he repeated his insistence the charges against him are fabricated.

"Mr President -- we cannot keep America great unless we aggressively protect and defend citizens wherever they are in the world," he said in comments carried by Russian news agencies.

"Please tweet your intentions."

Whelan's appeal was rejected.

"This absurd political kidnapping continues," he said. "I am innocent of the one and only charge against me -- a crime that never occurred."

He said "my life has been threatened, my rights denied" and that he had been isolated by officers in an attempt to extract a confession.

The defence team for Whelan, who also carries Canadian, Irish and British passports, has argued that he was framed by an acquaintance who passed him a USB drive that was supposed to contain vacation photos.

Whelan is among high-profile detainees mooted for a potential prisoner swap, possibly with Maria Butina, who was sentenced to 18 months' jail in the US last month after admitting to one count of conspiracy.

But a high-ranking Russian diplomat last month said swapping Whelan for Butina was "out of the question".