Mnuchin questions reported cost of flying on military jets Pentagon documents show it costs $25,000 an hour to operate a C-37.

 -- Treasury Secretary Steven Mnuchin sought to defend his controversial use of military jets for domestic business travel today, and challenged ABC News' reporting that it costs $25,000 an hour to operate the aircraft by suggesting the network check those figures with the Pentagon.

Pentagon documents show it costs $25,000 per hour to operate the Air Force's C-37 jet -- the same jet that flew Mnuchin from New York City to Washington D.C. on August 15.

"You can check with the Pentagon, because that's not what they charge," Mnuchin told "This Week" co-anchor Martha Raddatz. "But it costs a lot of money," he added.

According to Mnuchin's spokesman, it appears the secretary was referencing the reimbursement rate the Pentagon charges outside agencies to fly on its aircraft -- which is about $10,000 an hour.

While that figure is also accurate, it doesn't change the fact that it costs the Air Force -- and therefore the American taxpayer -- $25,000 an hour to operate the aircraft.

However, Mnuchin said in his interview that cost is "not the point," adding that he needed to fly on a military jet in order to make a secure phone call.

"I had a secure call that day that was critical, and set up, and needed to be done at that time," Mnuchin said. "And that's why I used the plane."

Mnuchin's travel habits -- including a business flight to Kentucky during the solar eclipse and a request for a military jet to take him and his wife on their European honeymoon, are under review by the Treasury Department's inspector general. Mnuchin says he welcomes the review and denies any wrongdoing.

ABC News' Elizabeth McLaughlin contributed to this report.