The United States on Thursday banned all flights of Pakistan International Airlines (PIA) with immediate effect.

The US Transport Department said in a statement that special permission given to PIA had been suspended due to safety concerns.

The information is contained in the revocation of special authorization dated July 1 provided by the department to Reuters on Friday.

Pakistan last month grounded almost a third of its pilots after discovering they may have falsified their qualifications.

The European Union Aviation Safety Agency suspended PIA’s authorization to fly to the bloc for six months in a blow to the carrier’s operations.

The move follows the grounding of 262 airline pilots in Pakistan over fake licenses in a decision made by the Civil Aviation Authority of Pakistan.

Pakistan’s Geo News reported PIA had confirmed the U.S. ban and said it would address the concerns through ongoing corrective measures within the airline.

This action was taken after Pakistan International Airlines (PIA) wrote to foreign missions and global regulatory and safety bodies, notifying them that it grounded all 141 pilots suspected of obtaining licenses through unfair means.

“It is also ensured that pilots flying PIA flights are having genuine licenses endorsed by the government of Pakistan and are in physical possession of the same during all domestic and international flights,” said a copy of the letter sent to the US Embassy in Islamabad.

Pakistan grounded at least 262 pilots, 109 commercial, and 153 airline transport pilots as an investigation to verify their license was initiated.

The 262 pilots include 141 from PIA, nine from Air Blue, 10 from Serene Airlines, and 17 from Shaheen Airlines, which has closed down.

Pakistan’s grounding of pilots with dubious credentials followed the crash of a PIA jet in May that killed 97 people.