Blackstone Group LP has agreed to buy about 6.4 billion euros ($8.7 billion) of mortgages from Catalunya Banc SA as it invests in Spain's economic recovery.

MADRID—Blackstone Group LP has agreed to buy about 6.4 billion euros ($8.7 billion) of mortgages from Catalunya Banc SA as it invests in Spain’s economic recovery, according to report Wednesday from Bloomberg News.

Blackstone was the winner in the process known as “Project Hercules” that began in April, said a Bloomberg source, who asked not to be identified because the information wasn’t public yet. El Confidencial, a news website, reported earlier Wednesday that Blackstone would pay 3.5 billion euros for the loans.

FROB, the fund that controls nationalized Spanish lenders is seeking a buyer for Catalunya Banc. Banco Santander SA (SAN), according to news reports.

Bloomberg said Andrew Dowler, a London-based spokesman for Blackstone, declined comment, as did a spokeswoman for the FROB.

The assets sold to Blackstone consist mostly of residential mortgages concentrated in the region of Catalonia, according to a sale document for the portfolio seen by Bloomberg.