An Uzbek-born Russian tycoon, Alisher Usmanov, says he is planning a libel lawsuit against Russian opposition leader and Kremlin critic Aleksei Navalny.
Usmanov says he has intentionally ignored what he described as "lies" by Navalny's anticorruption group.
But Usmanov told TASS on April 11 that Navalny had "crossed a red line" after he accused Usmanov of being involved in criminal activities.
In March, Navalny's anticorruption group published materials about Russian Prime Minister Dmitry Medvedev which included allegations that Usmanov had given away expensive properties for free to a foundation with alleged links to Medvedev.
Usmanov told TASS that all of his business activities are "legal and transparent," and that Navalny has "no moral right" to accuse him.
Navalny reacted to Usmanov's April 11 statement on Twitter by saying: "Alisher Usmanov, who served six years in prison in the Uzbek Soviet Socialist Republic, says that I am a 'criminal' and he 'will sue me.'"
Revelations in investigative reports by Navalny's organization led to anticorruption protests in Moscow and other Russian cities on March 26.
With reporting by TASS