US aviation regulators struck back at major carriers’ reliability Thursday after the head of United Airlines Holdings Inc. called the government’s air-traffic system “by far the No. 1” cause of flight delays. 

United Chief Executive Officer Scott Kirby made the comments in Washington during a conference. Within hours, the Federal Aviation Administration issued a statement, including a chart showing US airlines were responsible for more than twice as many minutes of delay as the agency through May of this year.

“The FAA’s mission is keeping airline passengers safe,” the FAA said. “Airlines should focus on restoring customers’ faith by being transparent about the cause of interruptions and by delivering what they promise.”

Delays and cancellations have surged this year as travel rebounded from the pandemic. Airlines, which have struggled with staff shortages and other issues, have been the biggest cause of the increase, according to data they report to the Department of Transportation.

The tense summer of delays led to fingerpointing, not only from airline officials including Kirby, but also by Transportation Secretary Pete Buttigieg and even President Joe Biden.