MOSCOW — Russia has threatened to block YouTube and Instagram if they do not take down videos and photos relating to Oleg V. Deripaska, an oligarch who was once close to President Trump’s former campaign manager, Paul Manafort.

A billionaire aluminum and mining magnate, Mr. Deripaska was the subject of an investigation published last Thursday on YouTube by the anticorruption activist and opposition leader Aleksei A. Navalny.

Mr. Navalny’s team scoured social media accounts belonging to a 21-year-old Belarus-born blogger, Anastasia Vashukevich, who posted videos in 2016 that showed Mr. Deripaska sailing on his yacht around Norway with a deputy prime minister, Sergei E. Prikhodko. At one point, Mr. Deripaska appears to be explaining to the blogger why relations between Russia and the United States are so bad. (Mr. Deripaska was an investor in a private equity firm controlled by Mr. Manafort, but the two men had a falling out.)

Ms. Vashukevich had written a tell-all book about her career as a model and escort, and claimed that a modeling agency hired her to spend time on Mr. Deripaska’s yacht. But her claims did not get widespread attention until Mr. Navalny’s inquiry was published.