Blackstone Group and Bain Capital are preparing a bid for all of Yahoo Inc that could value the Internet company at more than $20 (12.73 pounds) per share, with the participation of Yahoo's Asian partners, a source familiar with the matter said on Wednesday.

The potential bid by the consortium, which would include China's Alibaba Group and Japan's Softbank Corp, has not yet been finalized, the source and two other people familiar with the matter said.

The Chinese e-commerce giant, whose primary interest is in buying back the 40 percent stake in Alibaba owned by Yahoo, is still keeping its options open, and said it has not decided yet whether to participate in a bid for all of Yahoo.

Alibaba Group has not made a decision to be part of a whole company bid for Yahoo, Alibaba Group spokesman John Spelich said in an emailed statement on Wednesday.

Yahoo's shares, which closed at $15.71 on the New York Stock Exchange on Wednesday, gained 6.4 percent to $16.72 in after-hours trading, valuing the company at more than $20 billion.

A bid for Yahoo at more than $20 per share would mean a deal value of about $25 billion based on 1.24 billion shares outstanding shares, potentially making it the largest leveraged buyout in recent years.

Blackstone and Bain declined to comment, while Yahoo and Softbank representatives were not immediately available to comment.

Although a bid for all of Yahoo is not yet on the table, the latest twist turns on the heat on Yahoo's board, which has received at least two offers for a minority stake in the company according to people familiar with the matter -- one from a consortium of Silver Lake and Microsoft Corp and another by TPG Capital. Silver Lake, Microsoft and TPG have declined to comment.

Meanwhile, private equity firm Thomas H. Lee Partners is interested in buying the U.S. operations of Yahoo, people familiar with the matter told Reuters previously. Providence Equity Partners and Hellman & Friedman are also interested in a potential Yahoo deal. Thomas H. Lee, Providence and Hellman & Friedman have declined to comment on the situation.

Bain and Blackstone have a track record of teaming up for joint investments. In 2008, the two buyout firms, in a partnership with NBC Universal, bought the Weather Channel.

In 2006, the private equity firms teamed up for a $6 billion buyout of Michaels Stores Inc, the biggest U.S. arts and crafts retailer.

(Additional reporting by Greg Roumeliotis and Soyoung Kim in New York; Editing by Steve Orlofsky and Carol Bishopric)