LONDON — Britain's airline regulator is seeking to force Ryanair to pay compensation for flights that were cancelled or delayed by a series of worker strikes after Europe's biggest discount carrier said it wasn't required to pay thousands of claims under European Union rules.

The Civil Aviation Authority says it has begun enforcement action against Ryanair after the airline ignored the regulator's ruling that the strikes were not "extraordinary circumstances" as defined by EU rules. Airlines aren't obliged to pay compensation for delays caused by extraordinary events such as bad weather.

The regulator also says Wednesday that Ryanair has terminated its agreement with an arbitration service hired to settle disputes over compensation. As a result, anyone who has filed a claim will have to wait until the enforcement action is completed.