Hopes of establishing daily flights between Cardiff and New York City have been dashed after talks reportedly broke down.
Discussions had been taking place between Cardiff Airport and US carrier Delta to establish a link with JFK Airport in New York.
But now the airline says it has "no plans" to launch a service.
The Welsh assembly government said it is "committed" to an air link.
It added that is keen to provide routes for business travellers.
Delta declined to comment on reports that it had asked for the assembly government to underwrite any losses made by the service.
The possibility of a regular air service between Cardiff and New York has been talked about for years.
In 2001, fledgling airline Air Wales investigated the possibilty of running a transatlantic link.
And in 2002, it was understood a major American company was in talks to bring in a service between Cardiff and New York three times a week from 2003.
At the time, the then First Minister Rhodri Morgan claimed the flights would have a "significant effect" on tourism in Wales.
However, the link has never been established.
But the assembly government said it was committed to working with Cardiff Airport on the plans.
"We are keen to see the development of the scheduled route network, particularly those routes that will provide enhanced connectivity for business travellers," a spokesman said.
"We would like to see a direct transatlantic service, but in the meantime we were pleased that Aer Lingus recently increased the frequency of their Dublin services with onward connections to New York, Boston, Chicago and Orlando.
"Cardiff Airport is in regular contact with a wide range of airlines about route development opportunities, including direct transatlantic services.
"Any support that we provide to the airport or airlines needs to comply with state aid requirements.
"We are committed to providing a financial contribution to the airport's capital expenditure programme, to enhance the infrastructure at the airport, subject to state aid clearance."