MOSCOW (AP) — Russia's Foreign Ministry says a woman who was detained in the United States on charges of being a Russian agent is a political prisoner and must be released promptly.

The Russian government previously objected to Maria Butina's arrest this month, but its characterization of her as a political prisoner on Thursday raises the level of complaint.

The 29-year-old Butina has been accused of working to infiltrate the National Rifle Association and other U.S. political organizations before and after President Donald Trump's election.

Foreign Ministry spokesman Artem Kozhin said at a briefing: "Her arrest is motivated solely by the motives of the U.S. domestic and foreign policy, and therefore she is a political prisoner."

The U.S. government has often criticized Russia for allegedly holding political prisoners.