In a statement carried on Wednesday by the North's state-run Korean Central News Agency, Pak Jong-chon, the Chief of the General Staff of the Korean People's Army said the "use of armed forces is not the privilege of the U.S. only", indicating the regime could also resort to just action, if necessary.
He added "anyone can guess with what action" Pyeongyang will answer if the U.S. takes military action against the regime.
The North's threat came just hours after President Trump told reporters at a NATO summit in London that Washington could use force against the North if it must.
Touting the U.S. military as the most powerful in the world, President Trump urged the North's leader to honor their agreement to denuclearize.
The North Korean official said Kim Jong-un was "displeased" to hear Trump's remarks, and insisted the only thing preventing a physical conflict between the two sides is the close relations between the two leaders.
Observers say the North is conveying a strong message to the U.S., indicated by the timing of the announcement.
The North Korean official's remarks were made in the morning Eastern Standard Time, and during the day in Europe, where President Trump was attending the NATO summit, to make sure the message was heard loud and clear right away.
Lee Seung-jae, Arirang News.