A major system failure that left thousands of Delta Air Lines' passengers stranded around the world Monday is being blamed on the subsidiary of a major U.S. investor-owned electric utility.

The flight data failure stemmed from Delta Air Lines' Atlanta-based headquarters, the airline said, blaming an electricity outage for causing the global problem. It's an assessment that the utility company in charge of the regional power supply adamantly refutes.

Delta said an overnight electricity outage in Atlanta "impacted Delta computer systems and operations worldwide, resulting in flight delays," according to its website.

Southern Co. subsidiary Georgia Power disputed Delta's assessment, saying it was Delta that "experienced an equipment failure overnight that caused a power outage," according to USA Today. "Our crews have been out there all morning closely with Delta and their team as they repair the affected equipment. We don't believe it was a Georgia Power issue," a Georgia Power spokesman said.

The outage caused Delta's automated check-in system to go down, which forced the airline to scramble to manually check-in passengers. But the issue got worse.

As of 10:30 a.m., Delta said it had canceled about 300 flights "due to a power outage impacting Delta operations systemwide." It said it had operated 800 of its near 6,000 scheduled flights for Monday. "While systems are improving and flights are resuming, delays and cancellations continue," an update said.