Moscow (AFP) - Russian Foreign Minister Sergei Lavrov told his US counterpart Mike Pompeo on Saturday that the arrest of a Russian gun rights enthusiast on espionage charges in the United States was "unacceptable", his ministry said.

US prosecutors say Maria Butina, 29, exploited her close links with the powerful NRA gun lobby while posing as a visiting graduate student to endear herself with senior Republicans, guided by one of Russian President Vladimir Putin's major political supporters, Alexander Torshin.