President Trump says he knows more about the North Atlantic Treaty Organization than Secretary of Defense Jim Mattis.

"Frankly, I like Gen. Mattis. I think I know more about it than he does," Trump said during an interview with CBS News' "60 Minutes" that aired Sunday. "And I know more about it from the standpoint of fairness, that I can tell you."

Trump made the comments when asked whether Mattis, a former four-star Marine general, explained to the commander in chief that NATO was crucial to preventing World War III.

"The answer is this," Trump said. "I will always be there with NATO, but they have to pay their way. I'm fully in favor of NATO, but I don't wanna be taken advantage of."

Trump has repeatedly bashed the country's NATO partners for their slow progress in achieving the alliance's defense spending target of 2 percent of GDP by 2024.

[Also read: UK defense secretary: US strengthening its NATO role under Trump]

NATO was established in 1949 in the hope of promoting the national security of its membership against the Soviet Union after World War II and today remains a counter-force to potential Russian aggression.

In a clip of the same interview released earlier Sunday, Trump speculated Mattis "may" step down from his position within the administration because "he's sort of a Democrat" and "at some point, everybody leaves."

In response, a Defense Department spokesman, Col. Rob Manning told the Washington Examiner in a statement: "Secretary Mattis is laser-focused on doing his job — ensuring the US military remains the most lethal force on the planet."