Denmark's National Consumer Agency on Thursday published the names of six European airlines it said were still using illegal marketing practices, despite warnings from the European Commission after a review last year.

The Danish Consumer Ombudsman Henrik Oe said the Internet booking sites of Ryanair, Air Berlin, Air Baltic, SkyEurope, Aer Lingus, Brussels Airlines as well as that of Internet travel agent Seat24, contained incorrect information or made use of misleading booking procedures.

Of the 13 airlines carriers and ticket selling sites checked in Denmark in September last year, five have corrected the information stated on their web sites and one carrier no longer operates air services to Denmark, the Consumer Agency said in a statement.

European Consumer Commissioner Meglena Kuneva said in a statement she welcomed the publication of the names of the airlines.

"Europe's consumers are being let down by the airline industry. There are serious and persistent problems with ticket sales throughout the airline industry as a whole," she said.

In an investigation last year, the commission focused on practices such as misleading pricing and unfair contract terms in 16 member states and found 226 web sites in breach of EU consumer rules.

A mid-term follow up in May showed that around 80 companies had still failed to address the concerns expressed by Brussels.

Oe said that as the seven companies still in breach of EU rules in Denmark were based in other EU countries, authorities in their home countries would carry out further investigation.

Online booking is critical for the EU airline travel industry, which Commission figures show caters to some 700 million passengers each year.

"I hope operators have now realised the determination of the European Commission and national authorities to act on behalf of consumers where it is necessary," Kuneva said.