U.S.-based United Airlines says its computers are back up, but the carrier is still trying to resume normal operations after a glitch that disrupted many flights across the United States.

The airline said early Saturday on Twitter that the computer system is running again, several hours after the major disruption that began Friday.

United says the disruption grounded flights and stranded passengers for several hours across the U.S.

The airline said the problem disrupted departures, booking reservations and maintenance of its website.

United has not confirmed when it will resume normal flights, or how many planes were impacted at the height of the computer malfunction.