VIENNA (Reuters) - The United States is pressing Austria's Raiffeisen Bank International, the biggest Western bank in Russia, to drop plans to buy a 1.5 billion euro ($1.6 billion)industrial stake of a Russian tycoon, several people with direct knowledge of the talks said.

Washington's intervention is likely to derail one of the biggest Western deals in Russia since the start of the Ukraine war and piles more pressure on the Austrian group that handles billions of euros of international payments for Russians, two of the people said.

Raiffeisen is buying the stake in Vienna-based Strabag from a company the construction group identified as controlled by Oleg Deripaska.

The bank billed the deal, which is routed via Russia, as a means of unlocking some of the billions of euros stranded in Russia and potentially loosening its ties. The news in December prompted a rally in the bank's stock, which has been hit hard due to its Russia links.

In recent weeks, senior U.S. Treasury officials have underscored their concerns about the transaction in meetings with the bank and Austrian authorities, the people said. They pointed out that Deripaska is sanctioned.

U.S. government officials, who believe that Deripaska will benefit from the sale, have demanded the bank give details about the individuals and companies involved in the arrangement, the people said.

Should Raiffeisen press ahead regardless and the deal is proven to fall foul of U.S. sanctions, Washington could impose penalties on the bank, two of the people said.

In light of the U.S. position, one person said Austrian authorities would hold off on giving the green light, while another said the bank itself was preparing to drop the deal.

A spokesperson for the bank said it had "diligently verified the compliance of the Strabag transaction with all applicable sanctions, prior to signing" and had in recent weeks "briefed all relevant authorities, including the U.S. Treasury and OFAC (Office of Foreign Assets Control)".

"It goes without saying that RBI will not proceed with any deal which would be in breach of sanctions, or expose RBI to the risk of sanctions," said the spokesperson.

A spokesperson for Deripaska pointed to earlier remarks, where she said he had no control over the company holding the Strabag stake, describing the Western sanctions as misguided and based on false accusations.

CLOSE TIES

Two years after the outbreak of war, Raiffeisen's continued presence underlines the depth of relations between Austria and Russia, connected with Russian gas pipelines, and with Vienna serving as a hub for cash from Russia and former Soviet states.

The bank is a critical financial lifeline for millions of Russian customers who want to send euros or dollars abroad.

The conversations are taking place against a backdrop of continued scrutiny by regulators of Raiffeisen and its Russian connections, which started more than a year ago when U.S. sanctions enforcer OFAC started to look into the bank's Russia business.

The U.S. Department of Justice's Bank Integrity Unit, which is part of the criminal division, has also been looking into Raiffeisen over its Russia business, said one person familiar with the matter, who described the scrutiny as ongoing.

Another person said that a senior DOJ official had been in regular contact with the Austrian bank concerning Russia and had often visited Vienna in this regard. The Department of Justice declined to comment.

So far, key Austrian officials, irked by what they see as U.S. bullying of a small, neutral country, have fought the bank's corner because it is part of an influential industrial group that underpins the economy.

But two people familiar with government thinking said officials were not set on defending its latest deal over the stake in Strabag, which built the Olympic stadium for the Sochi winter games and luxury apartments in Moscow.

A spokesperson for the European Commission, which oversees EU sanctions on oligarchs including Deripaska, said it was aware of the transaction and "has asked for clarifications from the Austrian authorities, whose replies are pending".

The European Commission was "in close contact with the U.S. authorities", the spokesperson said, adding: "In general, under EU sanctions the assets of individuals and entities subject to asset freeze must be frozen, i.e. it is essentially prohibited to deal with those assets".

Recently, Austria pressured Ukraine to remove RBI from a Ukrainian blacklist, holding out on backing fresh EU sanctions on Russia until it did, people familiar with the situation have told Reuters.

Austria and RBI wanted it to be taken off Kyiv's "international sponsors of war" list, which sets out to shame companies doing business in Russia.

Although Italy's UniCredit also has a business in Russia and is similarly reluctant to leave, RBI is far larger and has become a test of Western resolve to end ties with Russia.

Russian authorities have made it clear to RBI, which has around 2,600 corporate customers, 4 million local account holders and 10,000 staff, that they wish it to stay because it enables international payments.

RBI had said it intended to spin off its Russian business, but two years into war, little has changed.

($1 = 0.9226 euros)

(Additional reporting Karen Freifeld in New York and Polina Devitt in London; Editing by Elisa Martinuzzi and Tomasz Janowski)