Election officials in Utah told US media they contacted the Gingrich campaign over the unpaid filing fee for the state's primary in June.

Utah election officials say the cheque bounced on 27 March. The fee must be paid by 20 April if Mr Gingrich is to qualify for the ballot.

 

Following Mr Santorum's departure on Tuesday, Mr Gingrich appealed for donations online.

"It is now a 2 person race," the former House Speaker tweeted, calling himself "the last conservative standing".

Mr Gingrich's campaign, which cut a third of its staff in March, told ABC News on Tuesday it was $4.5m in debt.

It was reported last month that the Gingrich campaign's latest fundraising tactic was to charge people $50 to have their photo taken with the candidate.