Nokia is the world's biggest mobile phone company

The company sponsored the talent show for the first three series but has now decided not to renew its contract.

Nokia's acting head of marketing Marcus Dacombe said he "wished the programme well" but no reason was given for the decision to end the deal.

On Wednesday, media watchdog Ofcom upheld a viewer complaint after ITV2 spin-off show The Xtra Factor appeared to promote Nokia in an episode.

The complaint related to an episode that showed X Factor Judges Simon Cowell and Louis Walsh jokingly sending childish insults via text message.

Ofcom said there were 13 close-up shots of Nokia mobile phone handsets, with the phone brand clearly visible.

Millions of people voted to crown Leona Lewis this year's winner

Xtra Factor producers said they used Nokia handsets "purely by chance", having used Motorola handsets in an earlier episode. But Ofcom noted the branding was not visible in most of the Motorola shots.

A second complaint about a Motorola phone being blurred on-screen on The X Factor was not upheld by Ofcom.

The show is now on the look-out for a new sponsor.

"This is a fantastic opportunity to be associated with one of the biggest entertainment shows on British TV," said ITV's brand partnerships director Gary Knight.

The programme recently escaped a fine for overcharging viewers by �200,000 for votes cast in its most recent series. A total of 1.3 million red button votes throughout the series were mistakenly charged at 50p instead of 35p.

Ofcom

Premium phone line watchdog Icstis reprimanded ITV for the error but did not impose a fine because the show's producers apologised and offered refunds.

Presenter Dermot O'Leary will replace previous host Kate Thornton on the new series of The X Factor, which starts this summer.

For the first time, contestants aged between 14 and 16 will be allowed to enter the competition.

Leona Lewis, winner of last year's series, reached number one with her single, A Moment Like This.