DELL'S largest independent shareholder has teamed with activist investor Carl Icahn in another challenge to founder Michael Dell's US$24.4 billion (S$30 billion) bid to take the struggling computer maker private.

Southeastern Asset Management and Icahn said in a May 9 letter to the Dell Inc. board that they want to let shareholders keep their stock and give them either US$12 per share in cash or additional shares in a deal that keeps the company publicly traded.

They said this option gives shareholders a stake in future gains made by the Round Rock, Texas, company.

An investment group led by Mr Michael Dell offered earlier this year to pay US$13.65 per share in a deal that would take the company private. Southeastern and Icahn criticised that proposal in a scathing letter to Dell's board outlining their latest offer.

"We want this board to hear from both Icahn and Southeastern loud and clear that it is insulting to shareholders' intelligence for the board to tell them that this board only has the best interests of shareholders at heart, and then accept Michael Dell's offer to purchase the company he founded for US$13.65 per share, a price far below what we consider its value to be," the letter states.

Dell spokesman David Frink said a special committee of the company's board is reviewing the letter from Icahn and Southeastern.

Icahn also has made a preliminary proposal to buy 58 per cent of Dell stock for US$15 per share.

Dell shares rose 9 US cents to US$13.41 in premarket trading an hour before the market opening.