Governor Robert Holzmann of the Austrian National Bank (ONB), which polices compliance with financial sanctions, told Reuters in an interview that the ONB believes the planned deal involving the biggest Western bank in Russia complies with sanctions.

However, he added: "Both the U.S. and Europe or Austria, the Austrian National Bank, we can't provide a blank cheque. We can't say 'Go ahead, you have the all-clear'. There's a tail risk which remains."

He declined to say what he meant specifically by a tail risk.

RBI has long been looking at selling or spinning off its business in Russia following the invasion of Ukraine.

It announced in December it planned to buy a stake in Strabag from Rasperia, a company controlled at the time by Russian tycoon Oleg Deripaska, who is under U.S. and EU sanctions. RBI says the deal complies with all sanctions.

Rasperia and that stake, now around 24% of Strabag, have since been sold to another company, Iliadis JSC, which RBI says is "an unsanctioned investor".

Reuters reported in March that Washington was pressing RBI to drop the planned 1.1 billion euro ($1.2 billion) deal.

"As the risk is there, it's a decision for Raiffeisen to say, given that there's a tail risk, is it worthwhile for us to do it or not?" Holzmann said.

In a statement on Tuesday RBI repeated that the planned deal complies with all sanctions requirements.

"Rasperia's new ownership structure should provide RBI comfort that no sanctioned individuals or entities will benefit directly or indirectly from RBI's announced acquisition of the Strabag SE shares, nor from any related payments for these shares."

($1 = 0.9291 euros)

(Writing by Francois Murphy; Additional reporting by Alexandra Schwarz-Goerlich; editing by Costas Pitas)

By Francois Murphy and Balazs Koranyi