All Southwest Airlines departures have been halted in the United States, officials said on April 18.

The Federal Aviation Administration (FAA) confirmed to The Epoch Times that a nationwide ground stop has been imposed.

“Southwest Airlines requested the FAA pause the airline’s departures,” an FAA said in an email.

It directed questions to Southwest Airlines, which did not immediately pick up the phone or respond to a request for comment.

On social media, the company said the stop stemmed from unspecified problems.

“We have had to implement a ground stop as a result of intermittent issues that were experienced, and we should hopefully be resuming our operation as soon as possible,” one post said.

“Technical challenges are unexpected and inconvenient for all, and you have our sincere apologies,” the company told one customer.

A Southwest pilot, who spoke on condition of anonymity to protect his job, said he received messages showing that the technical problem involved communication systems. Those systems are used during the process of weighing and balancing aircraft. They’re also used to relay weather and other information to and from airliners during flights, he said.

Customers reported flight delays and questioned when the flights would end up taking off.

Approximately 36 percent of Southwest flights were delayed on Tuesday, according to FlightAware. Southwest operates thousands of flights every day during peak travel periods, according to the company. It operates domestic and international flights.

This is a developing story that will be updated.