Frankfurt - German airline Lufthansa cancelled around 50 flights on Thursday ahead of a planned 24-hour walkout by cabin crew at six major airports on Friday as a long-running dispute over pay and conditions escalated.

As in previous walkouts, it was primarily domestic and European services that were affected, but a number of intercontinental flights were also hit, such as New York-Frankfurt and Hong Kong-Munich, according to the carrier's website.

Late on Wednesday, the cabin staff's labour union, Independent Flight Attendants' Organisation or UFO, said its members will stage a 24-hour stoppage Friday at the airports of Frankfurt, Berlin, Hamburg, Munich, Duesseldorf and Stuttgart in an escalation of their ongoing pay dispute.

Other much shorter walkouts of eight hours last week and earlier this week have grounded hundreds of flights and hit thousands of passengers.

Lufthansa has therefore said it will cancel 1,200 flights, or two-thirds of its total 1,800 flights on Friday.

According to its latest demands, the union - which represents some two-thirds of Lufthansa's 18,000 cabin crew - is seeking a five-percent pay increase backdated to April after three years of wage freezes.

It is also opposed to the use of temporary cabin crew on Lufthansa flights.

“We're prepared to go to mediation on the issue of pay hikes. But negotiations cannot include the use of temporary staff,” a Lufthansa spokesman told AFP.

“UFO has not contacted us so far,” he added.

The airline already faces headwinds because of rising fuel prices and fierce competition.

A 2009 strike by cabin crew cost Lufthansa tens of millions of euros.

In February, Frankfurt airport's apron control staff - traffic controllers who guide aircraft on the tarmac - walked off the job over demands for higher pay.

According to Peter Oppitzhauser, an analyst at Credit Agricole Chevreux quoted by Dow Jones Newswires, the first two days of walkouts have already knocked 2.0 percent off Lufthansa's annual operating result, which is seen at around 500 million euros this year.

Lufthansa shares were nevertheless showing a gain on the Frankfurt stock exchange early on Thursday, adding 1.48 percent to 9.79 euros in a generally firmer market. - Sapa-AFP