Michael Dell's $24.4 billion deal for Dell Inc., carefully crafted over six months, has gotten much more complicated.

Dell's board, seeking bids higher than last month's offer from the company's founder and Silver Lake Management LLC, has attracted interest from Blackstone Group LP as well as rival computer makers Hewlett-Packard Co. and Lenovo Group Ltd., said people familiar with the matter, who asked not to be identified because the matter is private. Billionaire Carl Icahn is also pushing the company to pay out a $9 a share special dividend.

With Dell's two biggest outside shareholders already opposing the deal, the fresh interest will only increase pressure on Michael Dell to raise his offer and consider alternative financial partners. While Dell's competitors are unlikely to bid, the people said, the company's shares have now risen well beyond the deal price to a nine-month high.