By Sinead Carew

NEW YORK (Reuters) - Sprint Nextel Corp raised its buyout offer for Clearwire Corp to $5 per share on Thursday and announced support from a key group of dissident shareholders, trumping rival suitor Dish Network Corp.

Sprint, already Clearwire's majority shareholder, also had Clearwire agree to changes in its governance rules, which could make it much harder for a rival bidder to buy the firm.

After the new offer, which was the result of Clearwire shareholder pressure and a rival bid from Dish, Clearwire changed its recommendation in favor of the Sprint deal and postponed a June 24 shareholder vote until July 8.

Sprint, the No. 3 U.S. mobile service provider, said the new bid gives Clearwire an enterprise value of more than $14 billion, or a roughly 14 percent premium over the value implied by Dish's bid to buy the minority shares for $4.40 each.

The latest offer will be the second time Sprint raised its bid since its December agreement to buy Clearwire's minority shares for $2.97 each.

Dish and Sprint have been fighting publicly over Clearwire since January. Clearwire has vast troves of valuable wireless airwaves that both companies want to use to help them compete in the wireless services market.

Sprint said it now has support from shareholders with 45 percent of Clearwire's minority shares, just shy of the more than 50 percent it needs to take over the company.

For example, Sprint said it has commitments from a group of activist shareholders that own about 9 percent of Clearwire's voting shares to support the deal.

These shareholders - Mount Kellett Capital Management LP, Glenview Capital Management LLC, Chesapeake Partners Management Co, Inc and Highside Capital Management LP - had teamed up to negotiate together for a higher price.

In addition, Clearwire promised to pay a break-up fee of $115 million if the current agreement was terminated.

Sprint raised its bid just a few days before shareholders in the smaller wireless company were due to vote on its previous $3.40 per share offer.

Shareholders had complained that Sprint's previous offer was too low even before Dish made its counterbid. Analysts and investors had said that Sprint would need to raise its bid or risk a contentious relationship with Dish as a minority shareholder.

Dish was not immediately available for comment.

The news came two days after Dish Chairman Charlie Ergen decided to back out, at least for now, from a battle with Japan's SoftBank Corp to buy Sprint itself.

Clearwire shares closed up 34 cents, or 7 percent, at $5.04 on Nasdaq. Sprint shares rose 7 cents, or 1 percent, to $7.07 on the New York Stock Exchange.

(Reporting by Sinead Carew; Editing by Gerald E. McCormick, Richard Chang and Bernard Orr)