Read more: Russian Stocks’ 33% Crash Is Fifth-Worst in Market History

UBS Group AG, meantime, triggered margin calls on some wealth management clients that use Russian bonds as collateral for their portfolios after cutting the lending value of some debt from the country to zero, people with knowledge of the matter told Bloomberg News. The Swiss wealth manager says it caters to half of the world’s billionaires.

One of the worst security crises in Europe since World War II threatens to deepen market declines in the region, but especially in Russia, which has been hit with sanctions by the U.S. and U.K. A handful of billionaires, including Gennady Timchenko, are also subject to penalties for their ties to Putin, though there are calls for widening the potential targets.

Read more: Here Are the Russian Billionaires Facing Sanctions Over Ukraine

“There are a lot of people in the U.S. and Europe who want to hit them directly,” Chris Miller, co-director of the Russia and Eurasia program at Tufts University’s Fletcher School, said of Russian billionaires in an interview. “I don’t think there’s any good news in the sanctions for them.”

Vagit Alekperov, the chairman of Lukoil, saw the sharpest decline in his net worth. It was slashed by almost a third in a day, falling by about $6.2 billion to $13 billion, according to the Bloomberg Billionaires Index. Shares of the Moscow-based oil producer slumped about 33% on Thursday.

Alexey Mordashov, chairman of the steelmaker Severstal, lost $4.2 billion on Thursday, bringing his fortune to $23 billion. Vladimir Potanin, president of Norilsk Nickel and currently Russia’s richest person, lost $3 billion.

Alekperov and Timchenko have each lost about $10 billion this year, or more than 40% of their fortunes. Those are the biggest percentage declines among the Russian billionaires tracked by the Bloomberg wealth index.