The White House has dismissed North Korea's claim that a tweet by Donald Trump amounted to a declaration of war.
White House spokeswoman Sarah Huckabee Sanders said the US had not "declared war" on Pyongyang.
The Trump administration also clarified on Monday that it was not seeking to overthrow North Korea's government after President Trump tweeted that its leader Kim Jong Un "won't be around much longer".
Pyongyang interpreted that tweet as a declaration of war.
In a speech last week to the United Nations General Assembly that if the US was forced to defend itself against North Korea, "we will have no choice but to totally destroy" the country.
The US and North Korea agreed to an armistice after the 1950-1953 Korean War, not a peace treaty. Because of that, they are still technically at war.
The Trump administration also said it was not advocating regime change in North Korea.
North Korea's top diplomat, foreign minister Ri Yong Ho, responded to that at the United Nations, telling reporters it was a declaration of war against his country by the United States, and that the North had the right to shoot down US warplanes in international airspace.
A senior administration official said Monday that the US policy was not regime change.
Mr Ri told reporters that Mr Trump's statement gives North Korea "every right" under the UN Charter to take counter-measures, "including the right to shoot down the United States strategic bombers even though they're not yet inside the airspace border of our country".
Mr Trump's tweet on Saturday said: "Just heard Foreign Minister of North Korea speak at U.N. If he echoes thoughts of Little Rocket Man, they won't be around much longer!"
Mr Ri said: "The question of who won't be around much longer will be answered then."
North Korea has repeatedly said it needs a nuclear deterrent because the US intends to invade it.
Mr Ri told the UN General Assembly on Saturday that the Pyongyang's recent "ICBM-mountable H-bomb test" was a key step to completing its nuclear force.
He called it "a war deterrent for putting an end to nuclear threat of the US and for preventing its military invasion".
"Our ultimate goal is to establish the balance of power with the US," he said.