SINGAPORE (Reuters) - U.S. asset manager BlackRock (BLK.N: Quote, Profile, Research) is to buy a portfolio of subprime mortgage debt from UBS (UBSN.VX: Quote, Profile, Research) for $15 billion (7.6 billion pounds), the Financial Times reported on its website on Tuesday, citing people familiar with the transaction.

The FT said the deal was due to be announced on Tuesday along with first-quarter results from UBS.

It said the debt would be bought by BlackRock at a 25 percent discount to its face value of $20 billion and then placed in a new fund that would be marketed to investors.

UBS would hold a minority interest in the fund, which would enable it to participate in any gains.

The FT said UBS declined to comment.

(Writing by Alan Raybould, Editing by Ian Geoghegan)