"Diplomats from the embassy have visited M.V. Butina… A note of protest has been lodged with the Department of State due to the unlawful court ruling. We call on the US government to ensure protection of rights and legal interests of our compatriot in compliance with international standards related to human rights," the embassy wrote in a Facebook page.
A US federal court sentenced Maria Butina last Friday to one and a half years in prison on charges of conspiring to act as a foreign agent in the United States.
In March, US authorities agreed to deport Butina but changed their decision shortly before the trial after a last-minute testimony from a former FBI employee was added, who claimed that Butina's activities were harmful to the US.
Maria Butina, 30, who has been held in US custody since mid-July 2018, pleaded guilty to a single count of conspiring to act as an unregistered foreign agent as part of a plea deal.
Russia has repeatedly insisted that Butina is innocent, saying she was forced to plead guilty under duress.
Commenting on the Butina case, Russian President Vladimir Putin said that her indictment was unjustified because she was not charged with working on a mission for the Russian government.