The United States has grounded flights across the country after a “communication issue” impacted traffic control centres, US Transportation Secretary Sean Duffy said.

“FAA [Federal Aviation Administration] technicians are investigating the issue. We will provide immediate updates as we have them,” Duffy wrote on social media.

The FAA said in a post on X that there had been a “temporary telecommunications outage” and that, as a precaution, all flights were being halted. International flights would be handled case by case, it added.

About 7,000 flights have been either delayed or cancelled due to the stop, according to FlightAware.

Some 4,042 flights were in the air, heading to US airports, when the ground stop was ordered, according to the tracking site Flightradar24.

The communication issue affects all 22 air route traffic control centres, which guide aircraft.

Homeland Security Secretary Markwayne Mullin told reporters there was no indication that the ground stop was triggered by a threat to the US. “Everybody’s safe. The flights are accounted for,” he said. “This is not another 9/11.”

President Donald Trump had been briefed, he added.

Asked whether a planned rollout of a new AI tool meant to help air traffic controllers could be to blame, Mullin said officials had not ruled it out. “You just can’t rule out anything at this point. We are going through that process,” he said.

The FBI does not believe a cyberattack or criminal activity caused the failure, Bloomberg reported, citing an official familiar with the matter.

The cited official said investigators were examining whether a software update could have caused the outage, though the cause had not been determined.

The disruption is the latest sign of strain on the US air traffic control system, which has ⁠been beset by equipment failures, communications problems and ⁠shortages of controllers, as the FAA tries to replace ageing infrastructure.

Congress approved $12.5bn for the overhaul last year, and the FAA and White House asked lawmakers on Friday for ⁠another $30.1bn.

This is the first nationwide US ground stop since January 2023, when a key FAA computer system malfunctioned. Before that, the last time had been after the September 11, 2001, attacks.

The FAA has not provided any indication of when the ground stop might be lifted.

This story is developing…