WASHINGTON U.S. Transportation Secretary Pete Buttigieg said the department is investigating why Delta Air Lines passengers remained on board a plane at the Las Vegas airport that sat on the tarmac in extreme heat on Monday, citing reports that the plane sat there for four hours.

"I want to know how it was possible for passengers to be left in triple-digit heat onboard an aircraft for that long," Buttigieg told Reuters Thursday, calling the issue "infuriating."

Delta said it is reviewing the incident and added that multiple passengers were seen by first responders, while a flight attendant and passenger were transported to a local hospital.

(Reporting by David Shepardson; Editing by Leslie Adler)