"There is no evidence of a cyberattack at this point, but the President directed DOT (Department of Transportation) to conduct a full investigation into the causes. The FAA will provide regular updates," Jean-Pierre said in a Twitter post.

Biden, speaking to reporters at the White House, said, "Aircraft can still land safely but not take off right now."

U.S. flights were grounded or delayed on Wednesday as the FAA scrambled to fix a system outage, with passengers told to check with airlines for updates.

The FAA said it had ordered airlines to pause all domestic departures until 9 a.m. ET (1400 GMT) to allow the agency to validate the integrity of flight and safety information.on.

(Reporting by Steve Holland and Susan Heavey; Writing by Doina Chiacu; Editing by Andrew Heavens)