North Korea has threatened to launch "merciless military strikes against the US aggressors" after its failed attempt to launch a missile at the weekend.
US President Donald Trump, meanwhile, has told reporters on the sidelines of the annual White House Easter Egg Roll that the rogue state has "gotta behave".
The isolated nation has trotted out three of its most senior officials overnight Australian time to amp up its war rhetoric against the US, according to news.com.au.
North Korea's deputy foreign minister, Sin Hong-chol, has told Al Jazeera that its army is on "maximum alert" after US Vice President Mike Pence visited the demilitarised zone between the two Koreas on Monday.
"The time of dictating orders by brandishing the US military might has gone," Mr Sin told the Qatar-based broadcaster.
The official made a passing swipe at Trump and his administration, referring to him not as the President but as a "businessman".
"If those businessmen in power in the US thought of intimidating us by any military or sanction threats - as the [Barack] Obama administration used to do and failed - they will soon find out such threats are useless," Sin said.
"If we notice any sign of assault on our sovereignty, our army will launch merciless military strikes against the US aggressors, wherever they may exist, from the remote US lands to the American military bases on the Korean Peninsula, such as those of Japan and elsewhere."
Trump has tried to use trade incentives to pressure China into doing more to stop North Korea's development of nuclear weapons, but Sin implied this tactic would not work.
"The nuclear weapon in our possession is not illusion; it is not a commodity that may be traded for American dollars, nor is it for sale. So it cannot be put on the negotiating table with the aim to rip it off," he said.
The country's deputy ambassador to the United Nations, Kim In Ryong, has called the US a "gangster" hellbent on "disturbing peace and stability".
He accused the Trump administration of turning the Korean peninsula into "the world's biggest hotspot" and creating "a dangerous situation in which a thermonuclear war may break out at any moment".
"If the United States dares opt for a military action ... the DPRK [Democratic People's Republic of Korea] is ready to react to any mode of war desired by the Americans," Kim told a news conference at the UN headquarters in New York.
"We will take the toughest counteraction against the provocateurs."
He said North Korea was acting in self defence and would respond to any threat of nuclear weapons or intercontinental ballistic missiles "in kind".
North Korea's vice foreign minister has also maintained the threatening language, telling the BBC there would be "all-out war" if the US took military action.
"We'll be conducting more missile tests on a weekly, monthly and yearly basis," Han Song-Ryol said.
Trump's remark that North Korea has "gotta behave" was made off the cuff on Monday when he was asked whether he had any message for North Korea or its leader, Kim Jong-un.
His comment comes after a tense weekend on the Korean Peninsula where the North celebrated the 105th birthday of its founding father, Kim Il-sung, with an elaborate military parade on Saturday that showed off its growing missile arsenal.
The triumphant procession, intended to show off the nation's military might, was followed by a major embarrassment for the current leader.
A ballistic missile test launched near a submarine base on the country's east coast failed seconds after lift-off Sunday morning.
The US provoked North Korea's ire when it sent a naval strike group, including aircraft carrier USS Carl Vinson and three guided-missile destroyers, to the region ahead of the anniversary, which is one of the biggest days on the country's calendar.
Pence visited the South Korean capital Seoul on Monday as part of a tour of Asia, where he warned the North not to test the resolve of the US President on military matters.
"The world witnessed the strength and resolve of our new president in actions taken in Syria and Afghanistan," the US Vice President said.
"North Korea would do well not to test his resolve or the strength of the armed forces of the United States in the region."
He said "all options are on the table" in response to North Korea and that the "era of strategic patience is over".
Two North Korean soldiers watched Mr Pence closely as he visited the demilitarised zone on Monday, with one taking photographs of the visiting leader.
White House spokesman Sean Spicer said Trump would not draw "red lines" over North Korea and he would continue to play his cards "close to his vest" in terms of his military strategy.
"The action that he took in Syria showed, when appropriate, this President will take decisive action," Spicer said, in reference to Trump's missile attack in April in retaliation to the Middle Eastern nation's use of chemical weapons against its own people.
Spicer also praised China for its "historic" decision to take a "much more active role" against North Korea through economic actions.
"I don't think there's anybody in the world who would not believe that North Korea's actions are both provocative and a concern," Spicer told reporters Monday afternoon.
The tension between the US and North Korea is like "the Cuban missile crisis in slow motion", international security expert Robert Litwak told The New York Times.
Pence will visit Australia on Saturday as part of his tour of Asia.