Activision Blizzard Inc shares rose on Monday after Warren Buffett said his company Berkshire Hathaway Inc had taken a 9.5% stake in the video game maker, which Microsoft Corp has agreed to buy for $68.7 billion.

Buffett revealed the approximately $5.6 billion stake on Saturday at Berkshire's annual shareholder meeting and said he may increase the stake above 10%.

Activision shares were up $2.22, or 2.9%, at $77.82 in morning trading, after earlier rising to $78.22.

The price remains well below Microsoft's proposed $95 per share takeover price for Activision, whose franchises include "Call of Duty" and "Candy Crush," reflecting investor skepticism that antitrust regulators will approve the merger.

Berkshire's investment appears to reflect Buffett's view that other investors are too pessimistic the merger will be completed.

Microsoft and Activision did not immediately respond to requests for comment.

Before the merger was announced on Jan. 18, one of Buffett's other portfolio managers at Berkshire had bought about $1.1 billion of Activision shares, but Buffett said the increased investment was his own.

"We want to be very clear that it was Warren Buffett's decision, ... and he doesn't know what the Justice Department is going to do, he doesn't know what the (European Union) is going to do," Buffett said. "One thing we do know is Microsoft has the money."

(Reporting by Jonathan Stempel in New York; Editing by Lisa Shumaker)