Time Warner Inc.'s (TWX) chief executive said on Thursday that news of a possible sale of a stake in its America Online (AOL) unit to Google Inc. (GOOG) and Comcast Corp. (CMCSA) was "market rumor."

Richard Parsons, on a visit to Hong Kong, also said there were no plans for a tie-up with Microsoft's search-engine technology.

• For more, watch Your World at 4 p.m. ET

Two sources told Reuters that web search engine Google Inc. and cable company Comcast Corp. were in talks to buy a stake in AOL, in a deal reportedly worth up to $5 billion.

"It's market rumors, and I can't curb market rumors," Parsons said at a luncheon on Thursday, declining further comment.

An investment would set the stage for an alliance marrying Time Warner's trove of programing and Google's popular search and e-mail services with Comcast's high-speed Internet portal and experience in cable video distribution and telecommunications.

It would also create a powerful new challenge to Internet media company Yahoo Inc. (YHOO) and software giant Microsoft Corp (MSFT).

Under one idea, Google and Comcast would jointly own half of the AOL web businesses, though Time Warner would retain a controlling stake, the Wall Street Journal reported in its Thursday edition.

Google and Comcast are valuing AOL's content business at about $10 billion, which implies a valuation of as much as $5 billion for the minority stake, the Wall Street Journal said.

One source close to the deal, however, told Reuters that Google and Comcast could make an investment in the entire AOL business, which would lift the deal value to more than $5 billion.

Google and Comcast face competition from Microsoft, which is also holding talks with AOL, one source told Reuters on Wednesday.

Time Warner, which has faced criticism over its strategy from billionaire investor Carl Icahn in recent months, sees AOL as a centerpiece to its future growth.

The talks between AOL, Google and Comcast progressed over the summer, but one source warned that the discussions were still in early stages and could fall apart.

AOL contacted Comcast earlier this summer and has held separate discussions with Google over potential investments, the sources said.

Google, which derived about 11 percent of its first-half revenues from a deal with AOL, has discussed with AOL interest in AOL's free Web-based services, such as instant messaging and programing. In addition, Google contacted Comcast last week over possible interest in executing a joint investment, one source said.

Since then Google and Comcast have discussed taking a joint minority interest in the online unit of Time Warner.

Google also has held discussions with Comcast on its high speed Web site strategy. Comcast aims to tap into the online advertising business as well as experiment in how it can translate its expertise in video distribution to the Internet.

Google and Comcast will have to move quickly as Microsoft continues its own overture to AOL. Comcast and Google have not yet drafted a formal plan to invest in AOL, the sources said. One source said the deal, albeit attractive to Comcast, was not "critical" to the company.

AOL's talks with Microsoft are much further along, one source said.

"Microsoft has had a head start," the source said. "There have been deal terms and term sheets."

Separately, myriad companies have contacted Time Warner over potential partnerships, including Yahoo Inc., but the Yahoo discussions have not progressed, one source said.

Yahoo was not immediately available for comment.