SkyWest Inc., the largest U.S. regional airline, suffered “an internal technical issue” that caused about 700 flight cancellations on Thursday with additional operational issues spilling into Friday.

SkyWest did not immediately elaborate upon the nature of the glitch, but said Friday in a statement that the issue had been resolved on Thursday evening. SkyWest operates regional jet flights for American Airlines Group Inc., Delta Air Lines Inc., United Airlines Holdings Inc. and Alaska Air Group Inc., with United its largest customer in terms of daily departures.

Shares of SkyWest fell 2.2% to $46.63 as of 11:45 a.m. in New York. The stock is up about 16% so far this year.

The carrier, based in St. George, Utah, canceled 372 flights on Friday, or about 15% of its schedule, according to FlightAware, an aviation data service. It has more than 2,300 daily flights in 236 cities and a fleet of about 480 aircraft.

“We apologize to customers for the inconvenience; we are working to minimize the impact on Friday’s schedule and to return to normal operations as quickly as possible,” SkyWest said.

The cancellations affected about 400 Delta flights and 106 Alaska flights, according to spokespeople for each airline.