Trevor Reed was convicted last year of endangering the lives of two policemen in Moscow.
A former US Marine who is serving a nine-year sentence in Russia was being transferred from a remand cell in Moscow on Friday to the Mordovia region which has a large number of tough, Soviet-era prisons.
Trevor Reed was convicted last year of endangering the lives of two policemen in Moscow while drunk, a charge he denied. He said the ruling was "clearly political", and Washington called the trial "theatre of the absurd".
Reed had remained in a remand cell after his conviction pending an appeal. That appeal was rejected and his sentence was upheld at a court hearing last month.
"This morning Trevor Reed was (taken) from Moscow, he will serve his punishment in one of Mordovia's (prison) colonies," Alexei Melnikov, a member of a prison oversight commission was quoted as saying by the RIA news agency.
The region of Mordovia is around 500 km (310 miles) east of Moscow. Paul Whelan, who is also a former US Marine, is serving a 16-year sentence in a jail in the region on espionage charges that he denied.
Russian President Vladimir Putin said before a summit with US President Joe Biden last month that he was open to a prisoner exchange deal. It is not known whether Whelan or Reed might be included in any prisoner swap.
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