Lufthansa made a key concession in talks with unions, and both sides agreed to a mediator as a 24-hour walkout that grounded half the airline's flights in Germany entered its final hours.

Europe's biggest airline on Friday agreed not to employ cheap contract workers in Berlin as cabin crew, meeting a key union demand, as their latest stoppage over pay and conditions grounded 900 flights.

Around 13 flights were also expected to be cancelled on Saturday due to the knock-on effects.

"Unilaterally, until further notice and without further preconditions, Lufthansa renounces the employment of external cabin crews" hired in the German capital, the airline's chief executive Christoph Franz said.

Flight attendants of temporary employment agency Aviation Power employed by the airline, "will be offered a full-time position with the Lufthansa group next year", the company said.

A management statement called the decision "a huge step".

Management and UFO, the Independent Flight Attendants' Organisation, also agreed that a mediator would help end the conflict so they could sign new wage agreements for cabin crews by Wednesday.

"We need a couple's therapist," Nicoley Baublies, the UFO head, said earlier Friday.

Until the mediator has reached a decision, there will be no more walkouts from Saturday, said Lufthansa on Friday night.

The latest strike began at midnight local time (22:00GMT Thursday) and so far "more than 100,000 passengers are affected", a Lufthansa spokesperson said earlier.

Frankfurt 'most affected'

Frankfurt airport, Lufthansa's main hub and Europe's third-busiest airport, was "most affected" by Friday's stoppages, the spokesperson said.

But the head of the striking UFO labour union insisted that the situation in Frankfurt nevertheless remained "relatively calm", as the carrier had obviously made better preparations this time round, which is the third separate day of walkouts since the industrial action began a week ago.

"On average, there are 1,800 Lufthansa flights during a normal day, around half of these flights will take place," said the Lufthansa spokesman.

"All German regions and all types of flights are affected," he said, including long-haul flights which in the past strikes have been the least disturbed by the stoppages.

The strike began at 22:00 GMT, but its effect overnight was minimal as there were no overnight flights scheduled.

Al Jazeera's Nick Spicer, reporting from Frankfurt airport, said that the airline had clearly done everything it could to take leverage away from the union.

"Some 55,000 text message were sent out to warn passengers, and many of them were sent on buses and trains."

The union, which described strike participation as "very high", claims it is the biggest strike in Lufthansa's history, but the airline itself refused to comment on the scope of the stoppage.

Source: Al Jazeera and agencies