The head of United Airlines Holdings Inc. apologized to US Transportation Secretary Pete Buttigieg after the carrier publicly faulted regulators for worsening flight delays.

Scott Kirby, United’s chief executive officer, said he reached out to clarify comments in a staff memo earlier this month. In it, a United executive said half of its delay minutes and the majority of cancellations over the prior four months were the result of actions by the Federal Aviation Administration to manage traffic and flight capacity.

That prompted a sharply worded rebuttal from the agency, which accused United of deceptively conflating traffic-control actions with steps taken in response to poor weather.

Kirby didn’t back down from the broader claim that flight disruptions have been largely out of the airline’s control, but said the specifics of United’s argument were misconstrued.

“I apologized to Buttigieg because that is not what we intended,” the CEO said Thursday on a conference call to discuss quarterly earnings.

Read more: United Air Cuts Growth Plans as Flight Disruptions Persist

United said July 15 that Chief Operations Officer Jonathan Roitman, the executive who wrote the earlier memo, would move to an advisory role and be replaced by Torbjorn Enqvist. The airline didn’t give a reason for the change.

The share of US flight delays caused by airlines, as opposed to weather or air traffic control, surged to about 58% -- the highest level on record -- this year through April, according to data reviewed by Bloomberg News. The number surpassed those that were late because of storms, the government’s air-traffic system and security glitches, based on the data that’s submitted by carriers to the US Transportation Department.

The numbers also showed there was some truth to airline claims that staffing issues at FAA air-traffic facilities had contributed to the problem.