President Donald Trump is again assailing North Korea Kim Jong Un, saying that he "will be tested like never before."

In an escalation of the war of words between the United States and North Korea, Trump sent a predawn tweet Friday saying, "Kim Jong Un of North Korea, who is obviously a madman who doesn't mind starving or killing his people, will be tested like never before!"

Kim Jong Un of North Korea, who is obviously a madman who doesn't mind starving or killing his people, will be tested like never before!

— Donald J. Trump (@realDonaldTrump) September 22, 2017

Trump's broadside follows a rare statement issued by Kim, branding the U.S. president as "deranged" and warning he will "pay dearly" for his threat to "totally destroy" the North if it attacks. Hours later, North Korea's foreign minister reportedly said his country may test a hydrogen bomb in the Pacific Ocean.