Microsoft said on Thursday it was investigating issues with its cloud services in the Central U.S. region, which had caused the grounding and cancellation of several flights.

Low-cost carriers Frontier Airlines, a unit of Frontier Group Holdings, Allegiant and SunCountry reported outages that affected operations.

While Frontier said a “major Microsoft technical outage” had hit its operations temporarily, SunCountry said a third-party vendor affected its booking and check-in facilities, without naming the company.

“The Allegiant website is currently unavailable due to the Microsoft Azure issue,” Nevada-based Allegiant said in a statement to CNN. Allegiant did not immediately respond to Reuters request for a comment.

Frontier cancelled 147 flights on Thursday and delayed 212 others, according to data tracker FlightAware. 45% of Allegiant aircrafts were delayed, while Sun Country delayed 23% flights, the data showed. The companies did not give details on the number of flights impacted.