(Reuters) - U.S. Transportation Secretary Pete Buttigieg spoke on Sunday with the CEO of Delta Air Lines ( DAL ), following the carrier's cancellation of thousands of flights since Friday due to a widespread IT-systems outage and as it continued to try to restore operations, a department official told Reuters.

Delta CEO Ed Bastian told customers on Sunday that the carrier had canceled 3,500 flights through Saturday. Flightaware said Delta on Sunday had canceled another 899 flights -- or 24% of its schedule. Buttigieg during the call reminded Bastian of the airline's responsibilities to customers and the department's enforcement role, the official added.