France’s civil aviation authority ordered airlines to cut flights by 40% at Paris-Orly Airport on Sunday evening after a breakdown in air traffic control systems disrupted operations.

In a statement, the Directorate General for Civil Aviation (DGAC) said the disruption required "regulation,” prompting a substantial reduction in scheduled flights. The authority did not specify the cause of the system failure.

The DGAC said its teams "are fully mobilized to restore normal operations as soon as possible.”

Paris-Orly Airport serves domestic and international flights, including routes to most European countries and the United States.

Flights to Spain, Denmark, Saudi Arabia, Italy, Germany, Austria, the Netherlands, Ireland and several French cities were canceled Sunday, while many others were delayed.

More than 33 million passengers traveled through Paris-Orly Airport last year, about half the number at Paris-Charles de Gaulle, according to figures released by the operator, Aeroports de Paris.