WASHINGTON, Dec 15 (Reuters) - The United States on Thursday targeted Russia's financial services sector and Russian businessman Vladimir Potanin, increasing pressure on Moscow over its invasion of Ukraine.Nornickel, the world's top palladium and refined nickel producer, was one of the biggest prizes in the post-Soviet carve-up of Russian industry in 1990s.The U.S. Treasury Department said Washington also imposed sanctions on Rosbank (ROSB.MM), a Russia-based commercial bank it said Potanin acquired earlier this year, along with 17 subsidiaries of Russian VTB (VTBR.MM), which was designated by Washington earlier this year."By sanctioning additional major Russian banks, we continue to deepen Russia’s isolation from global markets,” the Treasury's Under Secretary for Terrorism and Financial Intelligence, Brian Nelson, said in the statement."Today’s designations by the United States, together with actions taken by our international partners, will further inhibit the Putin regime’s ability to fund its horrific war against Ukraine.""