Stocks tumbled on Thursday after President Donald Trump doubled down on his warlike rhetoric toward North Korea.

The president in a short briefing with reporters on Thursday said his already unnerving "fire and fury" comments on North Korea may not have been harsh enough. He warned that the country should be "very nervous" because "things will happen to them like they never thought possible." The remarks are the latest development in growing tensions between Trump and North Korean leader Kim Jong Un.

"Frankly, the people who were questioning that statement, was it too tough? Maybe it wasn't tough enough," Trump said of his Tuesday warning that any threats from North Korea would be met with "fire and fury like the world has never seen" from the United States.

"Maybe it wasn't tough enough," he said. "They've been doing this to our country for a long time, for many years, and it's about time that somebody stuck up for the people of this country and for the people of other countries. So if anything, maybe that statement wasn't tough enough."

Trump declined to specify what would be tougher than "fire and fury" or whether he was considering a preemptive strike. "We don't talk about that. I never do," he said. "What they've been doing, what they've been getting away with, is a tragedy and it can't be allowed."

The sabre rattling between the U.S. and North Korea has shaken markets.

The Dow Jones Industrial Average fell by 0.93% on Thursday. The S&P 500 declined 1.45% and the Nasdaq dipped 2.13%. Safe haven gold was up 0.94%.

The president also addressed China's role in reining in North Korea and suggested he's using trade relations as leverage to try to spur China to action. "I think China can do a lot more, yes, China can. And I think China will do a lot more. Look, we have trade with China. We lose hundreds of billions of dollars a year on trade with China. They know how I feel. It's not going to continue like that. But if China helps us, I feel a lot differently toward trade, a lot differently toward trade," he said.

"The people of our country are safe. Our allies are safe. And I will tell you this North Korea better get their act together or they're going to be in trouble like few nations ever have been in trouble in this world," Trump said.

Asked whether he could offer any assurance to the American people who are anxious about the situation and the possibility of a nuclear war, Trump said they should be "very comfortable."

"If North Korea does anything in terms of even thinking about attack of anybody that we love or we represent or our allies or us, they can be very, very nervous," he said. "I'll tell you why. And they should be very nervous. Because things will happen to them like they never thought possible, OK? He's been pushing the world around for a long time."