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(The Hill) — The White House on Wednesday said it has not seen evidence of a cyberattack being the cause of a system outage at the Federal Aviation Administration (FAA) that has caused hundreds of flights to be delayed.

President Joe Biden was briefed on the outage and spoke with Transportation Secretary Pete Buttigieg on Wednesday morning, he said.

“They don’t know what the cause is,” Biden told reporters. “I told them to report directly to me when they find out. Aircraft can still land safely, just not take off right now. They don’t know what the cause of it is, they expect in a couple of hours they’ll have a good sense of what caused it and will respond at that time.”

White House press secretary Karine Jean-Pierre tweeted that “there is no evidence of a cyberattack at this point, but the President directed DOT to conduct a full investigation into the causes.”

The FAA posted at 6:30 a.m. that it was working to restore its Notice to Air Missions System, which informs pilots about closed runways, equipment outages, and other potential hazards along a flight route.

Planes that were already in the air were safe to land, but those still on the ground could not take off safely, the agency said. Planes were grounded until 9 a.m. while the FAA addressed the problem.

The issue caused the delay of hundreds of flights in the U.S.

It is the latest air travel issue domestically, coming roughly two weeks after Southwest Airlines canceled more than half of its flights over a three-day period after Christmas, leaving thousands of passengers stranded.