A deal would create a formidable, with whom AOL is also having separate .
The combination would marry Time Warner's trove of programming and Google's popular search and e-mail services with Comcast's high-speed Internet portal and experience in cable video distribution and telecommunications.
On Thursday, Time Warner's chief executive sought to quell talk of an alliance with the two companies.
"It's market rumors, and I can't curb market rumors," Parsons said at a luncheon in Hong Kong, declining further comment.
Comcast declined to comment. A Google spokesman declined to comment on the talks, adding, "Google and AOL have a healthy global partnership and AOL remains a valued partner."
One source warned that the discussions over a joint investment were still in its early stages and could fall apart. The deal would reportedly be worth up to $5 billion.
AOL contacted Comcast earlier this summer and has held separate discussions with Google over potential investments, the sources said.
Although Google's discussions over its interest in AOL's free Web portal were progressing, Google had contacted Comcast last week over possible interests in executing a joint investment, one source said.
Since then, Google and Comcast have discussed the possibility of making a joint minority investment in the online unit of Time Warner.
Google and Comcast 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.
Parsons also said Time Warner had no plans for an alliance with Microsoft.