Austrian authorities have urged Raiffeisen Bank International (RBI) to drop a deal linked to a Russian oligarch fearing a backlash from the United States, people familiar with the matter said, a blow to RBI's plans to unlock funds stranded in Russia.

RBI, the biggest Western bank in Russia, wants to buy a stake in construction group Strabag linked to Russian billionaire Oleg Deripaska for 1.5 billion euros ($1.6 billion), a contested deal that has renewed international pressure on the Austrian lender.

In recent weeks, Austrian central bank officials have warned RBI about the deal, cautioning it could backfire if the U.S. penalises the bank, said one person with direct knowledge of those discussions.

The central bank is responsible for oversight of Western sanctions in Austria and also watches for broader financial stability.

RBI is buying the stake in Vienna-based Strabag from a company the construction group identified as earlier controlled by Oleg Deripaska. The move had come under fire from the U.S. Treasury because Deripaska is sanctioned, exacerbating tensions between Washington and RBI, which is already under scrutiny from U.S. sanctions enforcement agency OFAC.

The sale is embarrassing for Austria, given international criticism of the country for being too friendly towards Russia.