The U.S. Embassy says officials have visited Paul Whelan at a notorious Moscow jail, and complained that Russia has yet to offer evidence to back up espionage charges filed against the former U.S. Marine more than three months ago.
The embassy made the statement in a Twitter post on April 5, but gave no further information about the visit.
"Yesterday, there was a consular visit to U.S. citizen Paul Whelan at Lefortovo," the tweet said. "Days and weeks have passed, but Whelan still remains under arrest without any sort of formal evidence."
"Everyone is hearing the statements from Russian bureaucrats that he was 'detained red-handed.' So where’s the evidence?" it added.
A former U.S. Marine, Whelan was arrested on December 28 in Moscow and charged with spying. He was working as a global security director for a U.S. auto-parts manufacturer at the time of his arrest.
Russian officials have released few details of the allegations.
His defense lawyer, however, has suggested his client was set up, saying he was handed a flash drive that he believed contained harmless personal material such as photographs but allegedly contained classified information.
U.S. officials have complained in the past that Russia was interfering with standard diplomatic protocol regarding consular access to Whelan.
In February, an embassy spokeswoman said that Russian authorities had not allowed Whelan to give a signed Privacy Act Waiver to the embassy, which was preventing the release of any information regarding the case.
If convicted, Whelan could face up to 20 years in prison. His family has said he is innocent and that he was in Moscow to attend a wedding.