Several major U.S. carriers, including American Airlines, Delta and United, grounded flights on Friday morning due to a communication issue, according to the U.S. Federal Aviation Administration.

The airlines issued “global ground stops” following a major IT outage that hit businesses around the world.

In an emailed statement to Newsweek, a spokesperson for American Airlines said: “We’re aware of a technical issue with CrowdStrike that is impacting multiple carriers. American is working with CrowdStrike to resolve the issue as quickly as possible and apologize to our customers for the inconvenience.”

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The airline said that flights already airborne will continue with their journeys but no more will take off.

“We are in contact with our planes currently in flight,” the airline spokesperson said.

In a follow-up statement, American Airlines told Newsweek: “As of 5 a.m. ET, we have been able to safely re-establish our operation. We apologize to our customers for the inconvenience.”

Cybersecurity company CrowdStrike and Microsoft have had major outages, which have had widespread effects on airlines, banks and media outlets around the world.

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In an emailed statement to Newsweek, CrowdStrike said that the problem was caused by a recent update, which it has since addressed.

“CrowdStrike is actively working with customers impacted by a defect found in a single content update for Windows hosts. Mac and Linux hosts are not impacted. This is not a security incident or cyberattack. The issue has been identified, isolated and a fix has been deployed,” the statement said.

The company referred affected customers to their support portal for the latest updates. It advised a workaround for affected users in a Reddit support thread.

U.S.-based Frontier Airlines said on Friday that the Microsoft outage had affected its systems.

“During this time booking, check-in, access to your boarding pass, and some flights may be impacted,” the company said on X. It said later that normal operations had been resumed.

Microsoft said its outage started about 6 p.m. ET on Thursday, Reuters reported, but issues have since been resolved.

The company said that it was continuing to deal with “the lingering impact” of the outage, per Sky News.

Newsweek reached out to Microsoft via email outside of regular working hours.

Secretary of Transportation Pete Buttigieg said in a statement on X, formerly Twitter: “We are monitoring technical issues at Frontier Airlines leading to cancellations and delays across their network. Our department will hold Frontier, and all airlines, to their responsibilities to meet the needs of passengers.”

Several other airports and airlines around the world have been affected by delays and disruptions, including in Australia, Europe and Asia.

The cause of the Microsoft outage is not yet clear.

In a series of updates on X over the last few hours, the company said that it was investigating “an issue impacting users ability to access various Microsoft 365 apps and services,” which are its cloud-based services.

The company said that “multiple services are continuing to see improvements in availability as our mitigation actions progress.”

Update, 7/19/24 6:52 a.m. ET: This article was updated with comments from American Airlines and CrowdStrike.