Flights delayed several hours Thursday as American Airlines moves to complete its single reservation system after its merger with US Airways.

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American Airlines’ flight delays because of computer problems came just weeks before the company completes its move to a single reservation system after its merger with US Airways.

The airline said that its latest problems on Thursday, which delayed flights for several hours, were caused by a network connectivity issue affecting various computer systems, including its website and airport check-in counters at three of its biggest hubs: Chicago, Dallas and Miami.

The issue prompted the Federal Aviation Administration to ground American Airlines and American Eagle flights to and from these airports under a ground-stop program that lasted for about an hour and 45 minutes.

American said it had fixed the problem, which it did not disclose, but was still investigating the cause. It ruled out an outside breach of its systems.

Flights resumed with delays that averaged a little more than an hour. Six regional flights were canceled, according to a spokesman for the airline.

Systemwide delays have become common. In April, hundreds of American Airlines flights were grounded because of a problem in the flight dispatch software that pilots have on their iPads.

United Airlines has had its share of problems in recent months. In July, a faulty computer router prevented the airline from checking in passengers, grounding its fleet. About 150 United flights were delayed in June because of another computer problem.

American is moving to complete one of the trickiest phases of its merger with US Airways. (Casey Norton, a spokesman for the airline, said the problem was not related to the merger integration work.)

American has met most of the major operational and technical goals related to its 2013 merger. In April, the airline received its single operating certificate from the FAA, meaning all flights now operate under the American call sign, which pilots use to communicate with air traffic controllers. The airlines also merged their frequent-flier programs.

But the final step is among the most critical in any airline merger. American must switch over all future reservations and passenger information from the system used by US Airways, called Shares, to the system used by American, called Sabre.

The airline wants to avoid what happened to United in 2012, when problems with its reservation systems led to months of delays and cancellations after its merger with Continental Airlines.

American has opted for a three-month “drain down” approach rather than a more abrupt overnight changeover. American started moving all reservations into a single passenger system in mid-July, and it expects the switch to be completed Oct. 17.