The Federal Aviation Administration (FAA) and the US Department of Transportation "will continue to be transparent here about the causes of the issue" said White House Press Secretary Karine Jean-Pierre after thousands of flights were canceled or delayed Wednesday following an hours-long nationwide grounding of departures due to a system outage.

Also Read: Flights resume gradually across US after system failure

Earlier Wednesday, the FAA announced that “normal air traffic operations are resuming gradually across the US” after a technical glitch in the FAA computer system caused flights all over the country to be suspended.

“Normal air traffic operations are resuming gradually across the U.S. following an overnight outage to the Notice to Air Missions system that provides safety info to flight crews. The ground stop has been lifted,” FAA tweeted.

However, it added: “We continue to look into the cause of the initial problem.”

Earlier Wednesday, it was announced that as a result of the glitch, 1,162 flights were postponed, according to FlightAware, and another 94 flights were canceled.

The FAA said later that some aviation services had returned to work, but the glitch had not been completely fixed.