Bertelsmann is valuing its stake in Sony BMG at $1.2 billion to $1.5 billion as the German media group escalates its efforts to pull out of the record music joint venture with Sony Corp, the Financial Times reported on Thursday.

According to the report, the companies were keen to reach an accord this summer, although both parties have yet to reach agreement on price. The price of the BMG stake would come down if Sony pledged to buy services from Bertelsmann, the paper noted.

Speculation that Bertelsmann wanted to walk away from the 50/50 JV has gathered pace over the past few months. The joint venture agreement on Sony BMG, struck in 2004, is due to expire in August 2009, and rumblings from within the Guetersloh-based Bertelsmann camp have suggested a deal will come before that time.

Hartmut Ostrowski, who took over as Bertelsmann chief executive in January, recently upped the ante, when he said in March, "We might take over 100%, or sell our 50% to Sony so that they have 100% or we might continue the joint venture," he said. "All three outcomes are possible."

Bertelsmann's chief financial officer Thomas Rabe has since reportedly met with at least two private equity companies to discuss the possible sale of its share.

Industry sources speculate that the exit of Maarten Steinkamp as president of Continental Europe for Sony BMG signalled a broader transition in power, which would see much of the European company's control shifted to the U.S. Bertelsmann declined to comment.