President Donald Trump has put North Korea "clearly on notice" that he will not tolerate certain actions, but will not telegraph US moves in advance.
The White House spokesman Sean Spicer responded at a news briefing on Wednesday (local time) to a question about an earlier Trump twitter post reading, "North Korea is looking for trouble. If China decides to help, that would be great. If not, we will solve the problem without them! USA".
Mr Trump's tweet followed a meeting with his Chinese counterpart Xi Jinping in Florida last week, where Mr Trump pressed Mr Xi to do more to rein in North Korea.
Mr Spicer said the President is "not one to go out there and telegraph his response".
"He has made it clear with respect to North Korea that their actions with respect to missile launches is not tolerable. The last thing we want to see is a nuclear North Korea that threatens the coast of the United States, or any other country".
Tensions have grown on the Korean peninsula, with talk of military action by the United States gaining ground following its recent strikes against Syria.
There are also concerns the reclusive North may soon conduct a sixth nuclear test.
North Korea's official Rodong Sinmun newspaper said the country was prepared to respond to any aggression by the United States.
The paper stated that their "Revolutionary strong army is keenly watching every move by enemy elements with our nuclear sight focused on the US invasionary bases not only in South Korea and the Pacific operation theatre but also in the US mainland".
South Korea's acting President Hwang Kyo-ahn warned of "greater provocations" by North Korea and ordered the military to intensify monitoring and ensure close communication with the United States.