The US Federal ⁠Aviation Administration said in a statement that the nationwide halt to departures, and delays to landings, at all US airports that began at about 4pm Eastern Time on Friday was caused by "a temporary telecommunications outage".

"Every flight has been accounted for and international flights will be handled on a case by case basis," the FAA added.

Here is what we know about the rare nationwide "groundstop" issued by the FAA.

• There is, as of now, no sign that the "telecommunications outage" that led to the sudden halt to all departures at US airports has been fixed.

• It remains unclear what caused the outage, but, according to , the former Oklahoma senator now leading the Department of Homeland Security, "there is no indication… that this was a nefarious attack".

• There have been 10,343 flight delays within, into, or out of the US so far, accoring to the website FlightAware, and 1,479 cancellations.

• This is just the second nationwide ​ground stop of all departures since the 11 September 2001 attacks. The previous one came in January 2023, when the FAA paused all ⁠domestic departures for less than two hours.

Nearly 7,000 flights across the United States were delayed or canceled on Friday, according to flight-tracking service FlightAware. Planes already ⁠in the air have been allowed to land, Reuters reprots, but those on the ground could not take off.

The disruption is the latest and most dramatic sign of strain on a US air traffic ⁠control system beset by equipment and communications failures, controller shortages and aging infrastructure.

The FAA's groundstop order, halting departures from all US airports, runs through at least 11 pm ET Friday.

Speaking to reporters outside the White House on the nationwide groundstop at all US airports, the US Homeland security secretary, , said: "Just to make sure we understand, there is no indication, and we had no reason to believe as of right now that this was a threat to the United States. This was a telecommunication outage throughout FAA."

The secretary added that there is no evidence, "yet that this was a nefarious attack; it is just a telecommunication outage, as of right now."

Asked if it might have been caused by AI or a cyber attack, Mullin incorrectly said that the last nationwide groundstop was "on 9/11" and sought to reassure the families of travelers that this outage was not part of a terrorist attack. "There is no reason to be concerned about your loved ones if they're flying," he said.

"As we investigate what caused this, you always got to assume that as many cyber attacks that take place, that you make that assumption – so, but as of right now, that's not known."

After restoring communications, so all airborne flights can land, Mullin said, "we're going to continue to work to find out what the root of the cause is."

"We're not ruling out anything at this point," Mullin added.

As we wait for clarity on what caused the nationwide groundstop of air travel to and from all US airports, you could do worse than read this weekend's New York Times Magazine cover story from James Fallows, a veteran journalist and pilot about whether the US air travel system "is eroding margins of safety".

Reports are steadily coming in from airports around the US, where passengers are confronting the sudden halt to all air traffic due to an as-yet-unexplained communications failure.

The Guardian's own Tom Johnson, our head of audience development, sends along this dispatch from Ronald Reagan Washington national airport, known as DCA.

Hundreds of passengers wait for news in a packed terminal at Ronald Reagan Washington national airport. Gate agents, along with most travelers in the terminal, refreshed their phones looking for updates, and attempted to change their flights. Nearly every seat is filled, with some people sitting on the floor and using their luggage as makeshift desks for their laptops.

The exact cause of the nationwide air traffic control crisis in the US is not yet known, but, as our colleague Marina Dunbar reported, last week the Federal Aviation Administration announced that the first digital air traffic control towers in the US were officially operational, bringing new technology first to smaller airports in Florida and Alaska as the Trump administration presses ahead with updating the country's aviation infrastructure.

The digital towers use advanced camera systems and digital displays to give air traffic controllers a continuous, 360-degree view of airport operations, including runways, taxiways and surrounding airspace, according to the agency.

The nationwide paralysis of the US air traffic control system, causing thousands of scheduled flights to be grounded and thousands more to be unable to land, has prompted a wave of anecdotal reports from passengers at airports.

This is just the second nationwide ​ground stop of all departures since the 11 September 2001, attacks. The previous one came in January 2023, when the FAA paused all ⁠domestic departures for less than two hours, Reuters reports.

Last year, ​Congress ​approved $12.5bn to fix ​the FAA's ageing communications system, and ​on Friday ‌the FAA ​and ​White House asked Congress for another $30.1bn to address other issues.

According to the tracking website Flightradar24, there are currently "3,100 airborne aircraft bound for US airports amid nationwide ground stop".

In addition to the grounding of all flights at US airports due to a communications issue affecting air traffic control, the US Federal ⁠Aviation Administration advised all airborne flights to circle along predetermined routes instead of landing, due to "equipment outages".

The US transportation secretary, former Fox News host Sean Duffy, has confirmed that all flights are grounded at US airports "following a communication issue impacting all Air Route Traffic Control Centers", in a statement posted on social media.

"FAA technicians are investigating the issue," Duffy added. "We will provide immediate updates as we have them."

Duffy's post on the social media platform X appeared beneath one he pinned in late September, which includes a video of himself touting the introduction of a "new air traffic management tool that saves YOU time, cuts back DELAYS, and makes your flying experience BETTER".

The US Federal ⁠Aviation Administration on ⁠Friday ​issued a national ground stop "due ⁠to extraordinary circumstance and reasons for safety" after ⁠the agency earlier reported ​serious ‌air traffic ‌control communications issues, Reuters reports.

Shortly before the ‌nationwide announcement, the FAA first halted traffic in Chicago due to air traffic control communications issues. ‌An agency notice posted on its website said: "All departing traffic should remain groundstopped until ​further notice." The FAA said international flights will be managed ⁠on a case-by-case basis.