All flights across the United States were grounded "due to extraordinary circumstances and for reasons of safety," the Federal Aviation Administration said in a statement.

The ground stop is in effect until further notice and "due a communication issue impacting all Air Route Traffic Control Centers," Transportation Secretary Sean Duffy said in a statement on X. Air Route Traffic Control Centers are responsible for all flights above 18,000 feet, ABC News reports.

There are 22 of those centers in the U.S. "Traffic should remain ground stopped until further notice," the FAA said in an advisory.