FILE PHOTO: An American Airlines Boeing 737 Max 8, on a flight from Miami to New York City, comes in for landing at LaGuardia Airport in New York, U.S., March 12, 2019. REUTERS/Shannon Stapleton

CHICAGO (Reuters) - American Airlines Group Inc said on Wednesday its teams were working to re-book customers due to fly on Boeing Co’s 737 MAX as quickly as possible after the United States banned the aircraft.

Europe and other nations had already stopped the planes flying due to safety concerns, following an Ethiopian Airlines crash on Sunday, five months after a Lion Air crash involving the same jet.

American, the largest airline in the world, operates 24 737 MAX aircraft.

Southwest Airlines Co , which has the world’s largest 737 MAX fleet with 34 jets, said it was waiving any fare-difference charges for customers who were seeking to switch to another aircraft following bans across much of the world.

The low-cost airline already does not charge a fee for changing tickets. The company said it is also waiving charges for fare differences following customer concerns about traveling on the jets.

American said it was notified by the Federal Aviation Administration (FAA) of its decision to ground the jets earlier on Wednesday.