This is causing flight delays and cancellations. We regret the inconvenience this is causing our passengers,” Lufthansa said on Twitter. Lufthansa owns carriers Austrian Airlines, Brussels Airlines, Eurowings and Swiss. In a separate statement on its website, Lufthansa recommended that passengers in Frankfurt avoid traveling to the city’s airport. Passengers with domestic flights can switch to Deutsche Bahn — Germany’s national rail service — for free until Sunday, the airline added.

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