Mr Case still holds more than $250m in Time Warner stock

Steve Case said the world's biggest media company had "failed to capitalize on AOL's potential".

"It would be best to 'undo' the merger by splitting Time Warner into several independent companies," Mr Case told the Washington Post.

Time Warner's shares fell by more than half following its merger with AOL in January 2000.

'Too complex'

Time Warner has proven to be too big, too complex, too conflicted and too slow-moving Steve Case, AOL founder and former Time Warner chairman

"Instead of propelling AOL to new heights, the association with Time Warner has weighed AOL down," said Mr Case, who was a leading architect of the merger and served as the combined company's chairman until 2003.

In the meantime, rivals such as Google and Yahoo had made "important strides forward", he told the paper.

"Time Warner has proven to be too big, too complex, too conflicted and too slow-moving - in other words, too much like a classic conglomerate - to seize new opportunities."

Time Warner's media businesses include the Warner Brothers movie studio, cable news channel CNN and Time magazine.

Mr Case stepped down from the board of the US company in October, but still holds more than $250m of Time Warner stock.

Microsoft talks

Writing in the Washington Post on Sunday, Mr Case said that he had proposed to Time Warner's board in July that the company should be split into four separate businesses - Time Warner Cable, Time Warner Entertainment, Time Inc and AOL.

Mr Case's plea for a demerger echoes similar calls from billionaire investor Carl Icahn, who leads a group of investment funds holding about 3% of the company.

Time Warner and software giant Microsoft are understood to have held talks earlier this year on how the two firms could work more closely together.

Analysts believe Microsoft is keen to buy part of AOL and merge it with its own internet business.

Internet media firm Yahoo last month said it had pulled out of talks to buy a stake in AOL.