Swiss banks have reportedly frozen $1 billion in the accounts of Russian metals tycoon Viktor Vekselberg over fears that they may be fined following U.S. sanctions against the businessman.

Vekselberg, Russia’s ninth richest man with an estimated net worth of $14.4 billion, was one of several Russian businessmen hit by U.S. sanctions this year for alleged meddling in the 2016 U.S. election and other “malign activity.” The tycoon has since been forced to cut his shares in foreign companies and repay more than $1 billion in loans made by European banks including JPMorgan, Credit Suisse and UBS.