U.S. private equity firm Centerbridge Partners is interested in the 315 UK branches being sold by state-backed Royal Bank of Scotland , a person familiar with the matter said on Tuesday.

Sky News, which first reported the interest, said Centerbridge had joined forces with another buyout firm - Corsair Capital - in recent weeks, but that it was unclear whether the duo would make a formal offer for the branch network.

RBS declined to comment. A spokesman for Corsair also declined to comment.

RBS was ordered by European authorities to sell the branches as a condition of its 45.5 billion pound taxpayer-funded bailout.

The bank is separating the branches and preparing them for an initial public offering, while also inviting interest. More than five parties have expressed preliminary interest, a person familiar with the matter said.

Reuters reported in October that Virgin Money and U.S. private equity firm J.C. Flowers were leading a small field of potential suitors to buy the branches - dubbed Project Rainbow - after Spain's Santander pulled out.

(Reporting by Steve Slater in London; Editing by Tim Dobbyn)