Butina has been accused of working with a high-powered Russian official and two unidentified U.S. citizens, trying to infiltrate a pro-gun rights organization in the United States and influence the United States’ foreign policy toward Russia.

Lavrov said the actions of the American authorities, who arrested Butina “on the basis of fabricated charges”, were unacceptable and called for her release as soon as possible.

Lavrov and Pompeo also discussed ways to improve bilateral relations on “equal and mutually beneficial grounds” after the leaders of the two countries, Vladimir Putin and Donald Trump, met in Helsinki on Monday.