Customers at airports across the United States reported long lines and frustrating wait times after a computer system used by multiple carriers went down on Monday afternoon, though the company behind the system says its service is now back online.

Sabre, a Texas-based software and data-solutions firm, has apologized for delays caused by the outage of its computer systems — which are used by carriers including American Airlines, JetBlue and Alaska Airlines for bookings and reservations, and described as helping the carriers "serve their passengers and operate efficiently."

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"Systems are back online and customers are reporting normal or close to normal operations," Sabre tweeted just before 3 p.m. on Monday. "We sincerely apologize for any resulting travel delays."

American Airlines, too, apologized to passengers affected by the temporary outage of its Sabre systems.

"Earlier today, Sabre had a brief technical issue that impacted multiple carriers, including American. This technical issue has been resolved. We apologize to our customers for the inconvenience," a spokesperson stated.

Passengers began reporting of outages in the early afternoon, with some reporting long lines and even "bedlam" as a result of the carriers' computer systems being down.

Representatives for JetBlue and Alaska Airlines were not immediately available to comment on the outages for Fox News.

Sabre also experienced a similar outage in late March, which temporarily delayed passengers and resulted in long lines at multiple major airlines across the country. That outage, too, was resolved within a few hours of systems going offline, though Sabre did not confirm whether March's technical outages were related to Monday's.

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On its website, Sabre, which is based in Texas, describes itself as a “software and data solutions to help airlines market themselves, sell their products in both the direct and indirect channels, serve their passengers and operate efficiently.”