The European Commission launched an investigation in 2013 into marketing schemes offered to airlines operating at Girona-Costa Brava and Reus airports, about 120 km from Barcelona.

Spanish public authorities subsequently offered the carriers additional marketing deals, which will now be included in the ongoing investigation.

"Through these additional marketing agreements, as well as through the other marketing agreements already under investigation, Ryanair and other airlines received payments in the form of 'marketing incentives' since 2004," the Commission said.

The EU competition enforcer said its preliminary view was that the marketing schemes might constitute State aid.

It will now seek feedback from interested parties before deciding whether the incentives comply with the bloc's state aid rules.

Companies have to pay back aid if this is found to be illegal.

(Reporting by Foo Yun Chee; Editing by David Goodman)