U.S. Defense Secretary Mark Esper said on Thursday that "rogue states" like Iran and North Korea demand the United States' constant vigilance.

Esper made the comment while speaking at "The National Defense Strategy at Year Two" event hosted at the Johns Hopkins School of Advanced International Studies in Washington. 

The Pentagon chief said that the recent U.S. action against Iran sent the message that Washington will not stand idly by when its troops and interests are threatened.

As he discussed the Trump administration's National Defense Strategy, Esper said it is designed to help the U.S. maintain a competitive advantage over adversaries such as China and Russia.

The remarks came amid continued deadlock and tensions between the U.S. and North Korea after the North threatened to unveil a new strategic weapon and take shocking action early this year.