Dan Hesse, Sprint Nextel's chief executive, confirmed on Wednesday that the struggling US mobile network operator had received "significant interest" from potential acquirers of its Nextel iDen unit, but also cast doubt on the prospects for any deal that would require the purchaser to raise additional capital.

Sprint, the third largest US mobile network operator, paid $36bn for Nextel Communications and its iDen 'push-to-talk' network in 2005 but has struggled since then to integrate the Nextel operations.

Speculation about a possible sale or spin-off of the Nextel unit first surfaced a year ago after Gary Forsee, Sprint's former chief executive and architect of the merger, was forced out by the board.

Most recently there has been speculation that Nextel might be sold to a consortium including private equity interests for about $5bn although most analysts have suggested such a deal was unlikely in the current credit environment.

On Wednesday, Mr Hesse acknowledged that while there has been considerable interest in the asset, a sale was not the company's only option and that any deal requiring a suitor to raise capital would be difficult in current market conditions.

"There is no question that if a bidder was relying on financing that's become more difficult," he said.

However, despite the credit crunch, Mr Hesse said he remained optimistic about closing a separate deal with Clearwire, the independent WiMax operator, by the end of the year. He said the venture partners were still "all systems go".

Sprint and Clearwire announced plans earlier this year to fold their WiMax operations into a new company which will also be called Clearwire but will be 51 per cent owned by Sprint Nextel.

Under the agreement, which has yet to receive regulatory approval, a group of investors led by Comcast, Time Warner Cable, Intel and Google plan to invest an additional $3.2bn in the venture.

Mr Hesse was speaking at the launch of the company's Xohm 4G wireless mobile broadband service.

Sprint Nextel and its partners plan to roll out the new high-speed network based on WiMax technology across the US over the next few years.