A Moscow court on Tuesday extended the detention of the former U.S. Marine Paul Whelan until March 29 on espionage charges, Interfax news agency reported.
Whelan, who holds U.S., British, Canadian and Irish passports, was detained in December 2018 and accused of spying.
Deputy Chief of Mission Bart Gorman last week called for Russia to free Whelan.
Whelan was detained by agents from Russia's Federal Security Service in a Moscow hotel room on Dec. 28 last year.
Moscow says he was caught with a computer flash drive containing classified information. Whelan says he was set up in a sting and had thought the drive, given to him by a Russian acquaintance, contained holiday photos.
He has been held in pre-trial detention while investigators look into his case.