Corporate raider Carl Icahn and other investors made a new offer Friday for US computer giant Dell, calling a planned private equity 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 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 to take Dell private in a $24.4 billion buyout -- $13.65 a share -- led by Michael Dell, with the investment fund Silver Lake Partners.

Icahn, who initially offered $15 per share for up to 58 percent of Dell shares, unveiled the new plan which would inject new capital, keep the company publicly traded, and offer a new slate of directors.

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."