A battle for US computer giant Dell heated up Friday as corporate raider Carl Icahn and other investors made a new offer and called a planned buyout led by company founder Michael Dell a "giveaway."

The investor group, which holds around 13 percent of Dell shares, said in a regulatory filing it would urge shareholders to reject the private equity buyout and opt instead for its "superior" recapitalization plan, keeping the company public.

Icahn has allied with Southeastern Asset Management to block plans announced this year and led by Michael Dell, with the investment fund Silver Lake Partners, to take Dell private in a $24.4 billion -- or $13.65 a share -- buyout.

Icahn, who initially offered $15 per share for up to 58 percent of Dell shares, unveiled the new plan, which would inject fresh capital and keep the company publicly traded in what is known as a leveraged recapitalization.

The dissident investors would offer a new slate of directors if the current board refuses to back the plan.

Under the Icahn plan, shareholders would get $12 a share, from Dell's cash and new debt, and retain their equity stake.

Icahn, in a letter to shareholders also filed with the Securities and Exchange Commission, did not place a value on the offer, but said it "is superior to the going private transaction."

In unusually harsh language, the document called the buyout plan "the great giveaway" and "insulting to shareholders' intelligence."

It said the buyout undervalues Dell and "amazingly allows him to purchase the company from shareholders with their own money."

"It does not take a mathematician to understand that $12.00 in cash and a stub equity component with, as outlined in our view, significant upside operating potential, is superior to only $13.65 in cash," the document said.

"The going private transaction leaves all of the upside to Michael Dell and an opportunistic buyout group with only their own interests in mind."

Icahn is known for hostile bids and efforts to take over companies he sees as undervalued.

Dell's special committee evaluating offers said it would study the Icahn plan.

"Consistent with the special committee's goal of achieving the best possible outcome for all shareholders, we and our advisors are carefully reviewing the potential transaction to assess the potential risks and rewards to the public shareholders," a statement said.

Rob Enderle, analyst with Enderle Group, said that "investors don't like complex plans" and argued that the Icahn "could do more damage to Dell's valuation, crippling the company, than the payout would provide benefit."

Enderle said going private appears a better option for Dell to revive its fortunes, and that the Icahn plan creates "a very high risk that Dell would fail as a company."

Dell shares rose 0.83 percent to close at $13.43.

Dell unveiled plans to go private in February, giving founder Michael Dell a chance to reshape the former number one PC maker away from the spotlight of Wall Street.

The move, which would delist the company from stock markets, could ease some pressure on Dell, which is cash-rich but has seen profits slump, as it tries to reduce dependence on the slumping market for personal computers.

Under the terms of the deal, Michael Dell, who currently owns some 14 percent of Dell's common shares, would remain chairman and chief executive and boost his stake in the company.

Additional cash for the deal would come from Silver Lake, a major tech investment group, and MSD Capital, a fund created to manage Michael Dell's investments. The plan also calls for a $2 billion loan from Microsoft.

Another bid for Dell came from Blackstone Group, but was later withdrawn.

The Dell special committee said in March the company faces a tough road ahead because of changes in the tech industry, with a shift away from PCs to mobile devices, and tough competition from other manufacturers.

Michael Dell said in a memo last month he would "invest for growth" and compete aggressively in new markets if his plan to go private succeeds.