Clearwire Corp agreed to sell the rest of the company to Sprint Nextel Corp for a slightly sweeter $2.2 billion offer, days after minority shareholders criticized the previous bid as too low.

The deal is one of the few options Clearwire has to survive in the long term, as it needs to raise more financing to upgrade its network and to keep the business afloat.

Sprint, the number three U.S. wireless carrier and already the majority owner of Clearwire, raised its offer by 7 cents per share to $2.97 per share.

Clearwire's shares slid 8.3 percent in premarket trade on Monday to $3.09. They had jumped nearly a quarter to close at $3.37 on Friday, on hopes of a higher offer.

Comcast Corp, Intel Corp and Bright House Networks LLC, three minority shareholders that among them hold about 13 percent of Clearwire's voting shares, had agreed to vote for the deal, Sprint and Clearwire said in a joint statement.

The deal has the unanimous backing of the Clearwire board but it was not immediately clear if Sprint could win the backing of enough of Clearwire's minority shareholders to complete the purchase.

Some shareholders have said Sprint should offer as much as $5 per share. Holders of at least 24.8 percent of Clearwire's outstanding stock, other than Sprint, need to approve the deal.

Sprint wants Clearwire's substantial spectrum to better arm itself against larger rivals Verizon Wireless and AT&T Inc.

Reuters reported earlier that Japan's Softbank Corp, which recently agreed to buy 70 percent of Sprint, would not consent to a bid of more than $2.97 per share.

(Editing by Rodney Joyce and Sriraj Kalluvila)