Interior Secretary Ryan Zinke on Friday dismissed scrutiny of his use of private and government planes for trips within the U.S. and abroad as “a little BS.”

Politico reported Thursday evening that Zinke used a private or military plane for travel in at least four instances. The revelation followed news that Health and Human Services Secretary Tom Price, EPA Administrator Scott Pruitt and Treasury Secretary Steven Mnuchin all spent taxpayer money on private or government planes for travel within the continental U.S. as well.

Before giving a speech at a Heritage Foundation event, Zinke addressed his travel.

“Before we get started, I’d just like to address, in the words of General Schwarzkopf, a little BS on travel,” he told the audience.

Zinke defended his use of private and government planes, arguing that they were the only options that would allow him to meet his schedule.

“Using tax dollars wisely and ethically is a greatest responsibility and it is at the heart of a good government,” he said. “And there are times, however, when we have to utilize charter services because we often travel in areas and under circumstances that we don’t have other flight options.”

He listed the three occasions on which he took a charter plane, and noted that he took a military plane to view wild fires in the U.S. with the agriculture secretary.

“All this travel was done only after it was determined by multiple career professionals at the department that no commercial options existed to meet the promulgated schedule,” Zinke told the audience on Friday. “The flights were only booked after extensive due diligence by the career professionals in the department’s general law and ethics division. Every time I travel, I submit the travel plan to the ethics department, that evaluates it line by line to make sure that I am above the law, and I follow the law.”

In one of the instances reported by Politico and the Washington Post, and mentioned by Zinke on Friday, the interior secretary took a flight from Las Vegas to the Kalispell, Montana. The plane, rented through a charter service, was owned by the executives of an oil and gas company and cost taxpayers $12,375. The night of that flight, he spoke at an event for Las Vegas’ new hockey team; he then flew to Montana, arriving at 1:30 a.m., where he spent the night at his private residence. Zinke spoke at a Western Governors’ Association event the next day.