Alaska Airlines has revealed that an "unexpected failure" of a critical piece of hardware caused an IT outage that led to its entire fleet being grounded.

The outage was a result of an unexpected hardware failure in Alaska's data centers and is not related to cybersecurity issues, the airline said.

Alaska Airlines warned of more flight disruptions on Monday after an unexpected failure of a critical piece of hardware at its data centers late Sunday forced it to halt all flights for about three hours.