* U.S. imposes toughest Russia sanctions yet over Ukraine
* Sanctions prevent new loans by U.S. lenders to targeted firms
* Sanctions include Rosneft, Novatek, Gazprombank and VEB
* The 4 have $32.3 bln syndicated loans maturing in next 5 yrs
By Sandrine Bradley
LONDON, July 17 (Reuters) - New U.S. sanctions imposed on Russia for its actions in Ukraine will make it more difficult for Russian companies to refinance existing international loans and has dashed hopes that Russia's syndicated loan market is reopening, bankers said on Thursday.
Washington announced its toughest sanctions yet on Wednesday, which directly target several Russian companies and financial institutions with close ties to Russian President Vladimir Putin.
The companies include Russia's largest oil producer, Rosneft , its second-largest gas producer, Novatek, its third largest bank, Gazprombank, and state-owned bank Vnesheconombank (VEB).
Thomson Reuters LPC data shows the four companies have a combined $32.3 billion of syndicated loans outstanding in the next five years, which could be difficult to refinance.
The move could also close the market for other Russian loans that are currently in the market and make it impossible to raise any new loans.
Gazprombank is the most immediate casualty of the fresh sanctions. The bank is seeking a $1 billion, one-year loan to refinance one of $1.2 billion that is due to mature in September.
Bank of America Merrill Lynch, Citi, Goldman Sachs and JP Morgan are among the consortium of international banks that lent it the maturing $1.2 billion.
Gazprombank said in a statement on Thursday that equity and long-term debt with maturities of 90 days or more from U.S. entities were affected.
This means that U.S. banks will be unable to lend to the $1 billon one-year loan that Gazprombank is currently seeking.
"At best there will be a very long pause on Gazprombank, but I expect in reality it will be off the agenda," a senior loan banker said.
It could simply repay the loan, as VEB did at the end of April with a $2.5 billion loan it had originally planned to refinance.
Slavneft, which is part-owned by Rosneft, has mandated Raiffeisen Bank International to arrange a new $500 million loan.
Rosneft is also in the market with a $2 billion oil prepayment deal that it is raising with Swiss energy trading company Vitol.
Banks were also due to sign a $1.5-2 billion loan for listed state-backed bank VTB before the new sanctions were announced on Wednesday.
That deal was set to re-open the Russian loan market, as it was the first Russian loan to include U.S. banks since Russia annexed the Crimea.
The deal is now expected to be put on hold as U.S. banks reassess their ability to lend.
"I suspect there will be delays on VTB; people need to digest the implications of what has happened," the senior loan banker said.
Slavneft and VTB were not immediately available to comment. Rosneft, Vitol and Raiffeisen declined to comment.
The new sanctions have come as a surprise to bankers who were working to reopen the Russian syndicated loan market, which has been effectively closed since March and is now likely to remain so.
"People thought the sanctions issue was disappearing in the rear view mirror, but it isn't," a second banker said.
"This winds the clock back to two months ago and reminds everyone that this is still a dynamic and expanding issue. I think banks could come back from this with an even more conservative approach to Russia," he added.
Although U.S. banks will be constrained by the new sanctions, some European banks with significant relationships with Russian borrowers are more bullish on continuing to lend.
"The sanctions will not have teeth for European banks ... We are legally unaffected," a third banker said.
Other European banks are less optimistic that the effect of sanctions will be limited to U.S. banks, which have billions of dollars of Russian loan exposure.
"It is very premature to assume it can be business as usual. Different institutions have different risk appetite ... but the final impact of these new sanctions will take time to work through," the second banker said.
European banks' risk appetite in such matters has been dented by the experience of France's BNP Paribas, which this month had to pay nearly $9 billion for breaking U.S. embargoes against Sudan, Cuba and Iran. U.S. authorities are also talking to Germany's Commerzbank and Deutsche Bank over their dealings with blacklisted countries.
The new sanctions have also put a question mark over a $1.94 billion Rosneft-BP prepayment facility that backs the long-term delivery of crude oil products between Rosneft and BP.
Banks, including Lloyds and HSBC, both of which have been punished by the United States in the past for sanctions violations, pulled out of the deal before it was signed on June 27.
Lenders including Deutsche Bank, Societe General and Bank of China funded the facility only a couple of days ago. Some banks have now asked lawyers to look at the loan agreement, which contains enhanced sanctions provisions that are designed to protect banks.
"Lawyers are looking at it (the Rosneft-BP loan) at the moment," the fourth banker said.
BP was not immediately available to comment. (Editing by Tessa Walsh and Will Waterman)