VOWING to look hard at signs of trouble inside the US air force's nuclear missile corps, Defence Secretary Chuck Hagel says it's clear "something is wrong".

Hagel told reporters that he is confident the problems will get fixed and that the country's arsenal of nuclear weapons will remain safe and secure.

He was commenting on the air force's dual investigations of drug use and exam cheating within its nuclear missile force, as well as a series of disclosures last year by The Associated Press about security lapses, leadership failures and other problems among those who operate and protect the Minuteman 3 missile force.

Hagel said he will convene a high-level meeting soon to probe the problems.

At a Pentagon news conference, he said the issues are complex and derive from a post-Cold War mindset that has reduced the focus on the nuclear weapons mission and led people to "just take for granted" that it will function correctly.

"This is cultural," he said, noting that the US military has been intensely involved in fighting wars in Iraq and Afghanistan for more than a decade - conflicts with little direct relevance to the role of nuclear warriors.

"Over the years I do think we have taken some focus off of the responsibilities of these very dedicated, very bright young officers" who operate intercontinental ballistic missiles, or ICBMs, stationed in five US states, he said.

On Thursday, Hagel announced that he also will assemble a small group of outside nuclear experts to study personnel problems within the nuclear force and to recommend remedies. He has not yet said who will serve on that panel.