Sec. John Kelly: Terrorism on US Planes Keeps Me 'Awake at Night'

Homeland Security Secretary John Kelly said Sunday a terrorist plot against American planes "keeps me literally awake at night," calling the threat "something that is very real."

In an interview on CBS News' "Face The Nation," Kelly said a successful strike at a U.S. plane would kill "hundreds and hundreds of people in one fell swoop."

"The … thing that keeps me literally awake at night is the threat against aviation," he said. "We know that would be the Super Bowl for the terrorists to knock down an air plane in flight, particularly if it was full of Americans."

"There are a number of plots that we're watching very, very closely— very sophisticated, very threatening, and the number-one thing in my mind is to protect the American people," he added, calling the "aviation threat… something that is very real."

On the issue of North Korea's threat to the nation, Kelly said "as long as they're on the other side of the world without a missile and a nuclear weapon to deliver against the United States, they're not much threat right now— except in the world of cyber. They're pretty aggressive when they want to be in cyber,."

"The instant they get a missile that can reach the United States, and they have a weaponized atomic device, nuclear device on it, we're at grave risk as a nation," he warned.

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