(CNN) — All flights from several major US airlines, including Delta, United and American Airlines, were grounded Friday morning due to a communication issue – part of a massive debacle impacting businesses worldwide.

The ground stop impacted all flights from the airlines, regardless of their destination, the Federal Aviation Administration said. As of mid-Friday morning, more than 600 flights into, out of or within the United States had been canceled, according to FlightAware.com.

“The FAA is closely monitoring a technical issue impacting IT systems at U.S. airlines,” the FAA posted on social media. “Several airlines have requested FAA assistance with ground stops until the issue is resolved.”

Live updates: Global tech outages hit airlines, banks and businesses

The CEO of CrowdStrike, a cybersecurity firm that has Microsoft among its clients, said the IT issue causing a global outage has been identified and a fix has been deployed.

The technical crisis is also affecting international airlines as well as mass transit in New York and Washington, DC; banking in Australia, South Africa, the United Kingdom and elsewhere, Hong Kong Disneyland and the Israeli health service.

American Airlines later said it had resolved the issue affecting its operations.

“Earlier this morning, a technical issue with a vendor impacted multiple carriers, including American. As of 5 a.m. ET, we have been able to safely re-establish our operation. We apologize to our customers for the inconvenience,” the American Airlines said in a statement to CNN.

It’s unclear how long the ground stop for the other airlines will last.

Their grounding comes after a significant Microsoft outage brought Frontier Airlines and some competitors to a standstill for hours on Thursday – though the ground stop for those airlines has since been lifted.

Earlier Thursday, Frontier said its systems had been impacted by the outage, and offered refunds to inconvenienced passengers.

Other competitors including Allegiant and SunCountry also said they were having difficulties, including with their booking, check-in and trip-managing functions online.

The FAA also announced Friday morning all Allegiant flights would be grounded.

On the Azure cloud software status report site, Microsoft said service went down for some customers in the central United States around 6 p.m. ET, “including failures with service management operations and connectivity or availability of services.”

The company said it determined the cause and is working to fix it. A company spokesman did not immediately respond to a request for comment.

A number of international airlines also reported tech disruptions on Friday, including Virgin Australia and Qantas, along with airports across Europe and Asia-Pacific.

This is a developing story and will be updated.

CNN’s Samantha Waldenberg contributed to this report.