May 25 (Reuters) - Sweden's indebted SBB on Saturday entered into a joint venture, SBB Social Facilities, for approximately 5.7 billion Swedish crowns ($534.36 million) with U.S. based Castlelake and supported by Atlas SP Partners.

SBB Social Facilities will use loan proceeds to acquire properties from SBB, to refinance debt to SBB and for certain external debt, according to the statement. ($1 = 10.6669 Swedish crowns) (Reporting by Urvi Dugar in Bengaluru Editing by Chris Reese)