Treasury secretary says honeymoon travel request was a matter of 'national security' Mnuchin said his office was concerned about his access to secure communications.

 -- Treasury Secretary Steven Mnuchin confirmed the ABC News report that he requested a military aircraft for his European honeymoon last month, but said it wasn’t a question of luxury for him and his wife.

“Effectively it was a portable office so I could be available and ultimately, we withdrew the request,” Mnuchin said, speaking at a conference sponsored by Politico on Thursday. “I’ve never asked the government to pay for my personal travel.”

Mnuchin said his office was concerned that he needed to have constant access to secure information and communication as he also sits on the president’s National Security Council.

“This had nothing to do with convenience,” he said. “This was purely about national security.”

The honeymoon took Mnuchin and his wife, Scottish actress and model Louise Linton, to a series of stops across Europe, including Scotland, France and Italy following their June wedding.

ABC News learned from officials familiar with the situation that the request for a U.S. Air Force plane, which an Air Force spokesperson said could cost roughly $25,000 per hour to operate, was submitted in writing by Mnuchin's office.

Officials told ABC News Mnuchin withdrew the request after being told it would look bad for a man worth more than $300 million to travel at taxpayer expense on a private trip, even if he needed secure communications.

Mnuchin received the support of President Donald Trump on Thursday, even as an inquiry has been launched by the Treasury Department's inspector general over the honeymoon request.

"I've known him a long time, he is a very straight shooter," said Trump of Mnuchin while speaking aboard his Air Force One on his way back to Washington, D.C., after visiting impacted by Hurricane Irma in Florida.

"It could be that he used a plane and he's paying for it," the president continued. "I don't know anything about it, I really don't. I just heard about it a little while ago."

Trump said Thursday that the inquiry had not diminished his opinion of the former Wall Street executive, saying he has "total confidence" in the secretary.

"I've known him for a long time," said Trump. "He's a very honorable man."

Mnuchin also took umbrage at the suggestion he and his wife later took a government jet to Kentucky for the purpose of viewing the solar eclipse in near totality rather than for official business. The Treasury Department said the Mnuchins would reimburse the government for Linton's travel costs, but that incident is also under review by the inspector general.

In his defense, Mnuchin claimed he wasn’t particularly interested in the rare astronomical phenomenon.

“I was like, the eclipse, so we got there and I was like really?” Mnuchin said. “I don’t have any interest in watching the eclipse.”

Mnuchin’s wife, however, sparked public uproar after that trip when she posted a photo on Instagram of the pair departing their government plane and publicly sparred with a woman who criticized the picture in the post's comments.

“Do you think the US govt paid for our honeymoon or personal travel?! Lololol. Have you given more to the economy than me and my husband?” she wrote.

She later apologized for her comments. Mnuchin did not address those comments on Thursday.

ABC News' Ben Siegel, Matthew Mosk, Luis Martinez and Devin Dwyer contributed to this report.