NBC News first reported the searches.
A federal task force has been looking into Russian oligarchs and the money trail that helps fuel Putin's invasion of Ukraine, and the task force is working to enforce U.S. financial restrictions imposed on Russia and its billionaires. A spokesperson for the task force declined to comment.
Vekselberg, a Ukrainian-born businessman, built a fortune by investing in the aluminum and oil industries in the post-Soviet era. According to U.S. Treasury Department documents, Vekselberg heads the Moscow-based Renova Group, a conglomerate encompassing metals, mining, tech and other assets.
He was one of the first Putin allies sanctioned in April 2018 by the U.S. Treasury Department in response to Russia's 2014 annexation of Ukraine's Crimean Peninsula. Vekselberg's assets in the U.S. are frozen, and American companies are barred from doing business with him and his entities.
In April, the U.S. government seized a 254-foot yacht owned by Vekselberg at a port in Spain. At the time, the U.S. Justice Department asserted that the yacht could be forfeited for violations of U.S. bank fraud, money laundering and sanctions laws.
All the properties searched Thursday are owned by Vekselberg's childhood friend Vladimir Voronchenko or companies tied to Voronchenko's family and associates. Voronchenko was the founding director of a St. Petersburg museum built to house the oligarch’s Faberge egg collection.
Among the properties were four luxury condominiums on Fisher Island. Three were purchased for a combined $42 million but are worth considerably more today, property records show. Two are owned by The Medallion Inc., a Panama-registered company that lists Voronchenko's wife, Olesya Kharlamova, as a director.
Kharlamova, who like her husband was born and raised in Ukraine, is also an officer of a condominium association for two luxury high rises on Fisher Island, which is so favored by jet-setting Russians that they've been dubbed the “Red Zone” by other residents. Amenities include infinity-edge pools, a state-of-the-art theater and a fur coat storage facility to protect garments from Miami’s humidity.
In New York, Medallion Inc. in 2008 paid nearly $11 million for a penthouse unit at 515 Park Avenue in Manhattan and $11.4 million for the Southampton home. Both were searched Thursday.
Voronchenko's family and associates did not immediately respond to a call placed to them seeking comment.
Goodman reported from Miami.