Germany's consumer centres have confronted growing anger over price hikes for domestic flights after low-cost carrier Air Berlin went belly up in August. "A noticeable increase in complaints over ticket prices," has been recorded, Klaus Mueller, head of the Federation of German Consumer Organizations, told dpa.

German airline Lufthansa took over the bulk of Air Berlin's operations after the collapse of the low-cost carrier - formerly Germany's second largest. The collapse left a gap of tens of thousands of previously offered seats. Germany's cartel authorities announced an audit of Lufthansa at the end of November.

The company said it has not changed its price structure since Air Berlin's demise and that higher average prices resulted from greater demand. Mueller said he welcomed the fact that the Federal Cartel Office was reviewing pricing at industry-leader Lufthansa through its ability to examine the relevant documents.

"After that of course we also expect that consequences will follow and prices will be refunded if need be," Mueller said. No one claims that flying is cheap, Mueller said, "but it should also not be the case that Lufthansa mops up a monopoly profit."