The US Department of the Treasury has issued a formal warning to Austria’s Raiffeisen Bank International, indicating that its access to the US financial system might be restricted due to its business ties with Russia, according to Reuters. According to the agency’s source, on May 6, Deputy Treasury Secretary Wally Adeyemo sent a letter to RBI expressing concerns over the bank’s expansion in Russia, as well as a $1.5 billion deal with a sanctioned Russian magnate. Although the deal involving Oleg Deripaska was canceled by Raiffeisen a few days after receiving the letter, the source said that th…