Tensions are rising amid reports Pyongyang may be preparing another nuclear or missile test.
Its Foreign Minister Han Song-ryol said the US and its President Donald Trump are making trouble in the region by moving an aircraft carrier strike group into Korean waters and participating in joint military exercises with South Korea.
He also said the country will continue developing its nuclear program and conduct its next nuclear test whenever its leaders see fit.
Meanwhile China, North Korea's only backer, feared conflict could cause the regime to collapse and create problems on its border.
Chinese Foreign Minister Wang Yi warned that conflict "could break out at any moment" and said if war occurred there could be no winner.
Mr Wang's comments come as the US voices increasing concern at North Korea's development of nuclear weapons and deploys a Navy carrier group off the Korean peninsula.
Mr Wang said: "One has the feeling that a conflict could break out at any moment.
"I think that all relevant parties should be highly vigilant with regards to this situation."
"We call on all parties to refrain from provoking and threatening each other, whether in words or actions, and not let the situation get to an irreversible and unmanageable stage."
Adding to Chinese unease, Mr Trump said on Thursday that "the problem of North Korea" would be "taken care of".
"If China decides to help, that would be great. If not, we will solve the problem without them! USA."
The North Korean military responded on Friday by saying it would "mercilessly foil" any US provocation.
"Our toughest counteraction against the US and its vassal forces will be taken in such a merciless manner as not to allow the aggressors to survive," read a statement from the army, reported in English by North Korea's official news agency, KCNA.
Washington is concerned North Korea might develop the ability to launch a nuclear weapon at the US.
Mr Trump and China's President Xi Jinping have been in contact by phone since their summit last week in Florida, and Reuters quotes US officials as saying tougher economic sanctions against North Korea are also being considered.
China is concerned any conflict could lead to a huge refugee problem on its border with North Korea. It also fears the collapse of the North Korean regime, which would remove a buffer between China and a country with US military bases, and has thus long been wary of pushing Pyongyang too hard.
But, in a sign of growing frustration with its neighbour, it recently blocked coal imports from the North. And Chinese state broadcaster CCTV reports that the government will suspend direct Air China flights between Beijing and Pyongyang from Monday 17 April.
There is also intense speculation that North Korea could carry out a sixth nuclear bomb test or another missile launch - possibly a long-range missile - on Saturday.
However, North Koreans placed flower baskets and bouquets below portraits of founder president Kim Il Sung on Friday, showing little sign of tension despite fears the reclusive nation may conduct a nuclear test and the United States would retaliate.
The 105th birth anniversary of the founder is on Saturday, celebrated as the Day of the Sun in North Korea, its most important holiday. The North Korean regime often uses such anniversaries for displays of military prowess.
A light rain fell in the capital, Pyongyang, as people wearing gumboots and holding umbrellas walked past portraits of the late leader and signs proclaiming "Sun Day is the most significant event in North Korea".
Photo: AFP North Korea Foreign Minister Han Song Ryol. (file photo)