ANKARA 

Air traffic operations are resuming gradually across the US following a systemwide computer failure, the Federal Aviation Administration’s (FAA) said Wednesday.

"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.

"We continue to look into the cause of the initial problem," FAA wrote on Twitter.

Transportation Secretary Pete Buttigieg said there was no evidence of a cyberattack after flights were temporarily grounded.

President Joe Biden was briefed on the FAA’s outage by Buttigieg and Biden directed the Transportation Department to investigate, said a White House spokeswoman.

"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 will provide regular updates," Karine Jean-Pierre wrote on Twitter.

"Operations across the National Airspace System are affected," the FAA said earlier on Twitter, noting that it was working to restore the system.

"We are performing final validation checks and reloading the system now," it added.

The FAA provides air traffic services to more than 45,000 flights daily carrying 2.9 million passengers in the National Airspace System, according to its website.

The system is an airspace network that includes air navigation facilities, airports and landing areas.

The FAA had ordered airlines to halt domestic departures until 9 a.m. Eastern Time (1400GMT) to enable the agency to "validate the integrity of flight and safety information," it said in a separate Twitter post.