Carl Icahn, stepping up his battle against Time Warner Inc., on Tuesday unveiled details of his plan to shake up the media conglomerate, saying it should be split into four separate public companies.

In a report prepared by his investment-banking adviser Lazard Ltd., Icahn also said Time Warner should extend its share buyback plan to a total of $20 billion worth of stock through a series of "Dutch auction" tender offers.

Lazard said in a press release that the proposals could create about $40 billion in "incremental value" for Time Warner shareholders. Time Warner's stock price could reach between $23.30 and $26.57 a share, it said. The shares traded recently down 1 percent, or 16 cents, at $18.40 a share, giving the company a market capitalization of about $86.5 billion.

Icahn, who is leading an investor group with more than 3 percent of Time Warner's shares, is seeking to overthrow Time Warner's board at its annual meeting in May. He has tapped Frank Biondi, Jr., the former chief executive of Viacom Inc. and Universal Studios Inc., to take over as Time Warner chief executive if his proxy battle succeeds.

The proposals in the Lazard report detail ideas that Icahn already has been pushing. Icahn, who began his campaign against Time Warner in August, urged the company to immediately buy back $20 billion of its shares and spin off 100 percent of its cable business, rather than the 16 percent of Time Warner Cable the company plans.

More recently, after he retained Lazard, Icahn floated the breakup proposal.

Under the plan outlined Tuesday at a briefing in Manhattan, Time Warner shareholders would have a direct ownership stake in the newly created Time Warner, which would include the company's cable-TV networks and filmed entertainment divisions, as well as stakes in three new public "pure-play" companies: AOL, publishing and Time Warner Cable.