Ryanair may abandon discussions about new routes out of Belfast International Airport because of a disagreement with owners TBI over "favourable terms for airport charges and fees".

Industry sources say the low-cost operator is frustrated over a lack of progress at the negotiating table with TBI, which is also believed to be in talks with rival no-frills airlines Easyjet and Go about extending their services from Belfast International.

Ryanair currently operates flights from the City of Derry Airport to London Stansted but has no operations at Belfast International Airport.

The low-cost operator could deliver strong traffic growth for TBI, which will lose the majority of its BMI British Midland and all of its British Airways business later this month.

BMI British Midland plans to relocate all of its Northern Ireland operation, with the exception of four daily services between Belfast International and Heathrow, to Belfast City Airport in the next three weeks.

Aer Lingus has also ended its services between Belfast International and Shannon.

Mr Keith Brooks, chief executive of TBI, has confirmed that it is in discussions with a number of airlines about new routes, but declined to comment on the nature of the talks.

It is understood Ryanair is pushing for a deal that, according to industry sources, TBI believes is not economically viable for Belfast International Airport. Ryanair is renowned for its aggressive stance when it comes to negotiating on charges and fees.

One source at Belfast International Airport said the low-cost operator's demands could jeopardise the existing contracts with other no-frills airlines at the airport.

"While TBI would dearly love to get Ryanair on board, there is no way they are going to agree to a deal that would upset existing carriers," said the industry insider.

One of the major attractions that securing Ryanair holds for TBI is the prospect of increasing the number of direct services it offers from Belfast International to European destinations.

Easyjet's decision earlier this year to introduce a direct service to Amsterdam from the airport has proved to be a big success for the airline.

In the first four months, it carried 40,000 passengers.

Ryanair is looking at operating up to 12 flights a day from Belfast, including direct services to Paris and to Charleroi, its new Brussels hub.