North Korea has vowed to carry out weekly missile tests, after the US vice president warned that America’s “era of strategic patience” was over.
Han Song-Ryol, North Korea’s vice foreign minister, warned that “all out war” would result if the US took military action.
"We'll be conducting more missile tests on a weekly, monthly and yearly basis," he told the BBC.
His comments came as Mike Pence, the US vice president, arrived in Asia and visited the demilitarised zone between North and South Korea, and warned North Korea not to “test” President Donald Trump.
"Just in the past two weeks, the world witnessed the strength and resolve of our new president in actions taken in Syria and Afghanistan," said Mr Pence.
"North Korea would do well not to test his resolve or the strength of the armed forces of the United States in this region."
He reiterated US support for South Korea, telling his host: "We are with you 100 per cent."
Meanwhile, President Donald Trump weighed into the situation from the White House, where we was attending the annual Easter Egg Roll on Monday.
Asked for his message to North Korea after its failed missile launch on the weekend, Mr Trump said "They gotta behave". Pressed on his next move, he later said "You'll see".
Sean Spicer, the White House press secretary, told a briefing on Monday that the president would not be "drawing any lines in the sand" on North Korea.
"He holds his cards close to the vest. I think you're not going to see him telegraphing how he's going to respond to any military or other situation going forward. That's just something he believes has not served us well in the past," Mr Spicer said. "So I don't think that you're going to see the president drawing red lines in the sand. I think the action that he took in Syria shows that when appropriate, this president will take decisive action."
Mr Pence arrived in Tokyo on Tuesday for talks with Japanese prime minister Shinzo Abe. Mr Abe called for a peaceful resolution to tensions surrounding North Korea.
"It is a matter of paramount importance for us to seek diplomatic efforts as well as peaceable settlements of the issue," Mr Abe said.
"At the same time dialogue for the sake of dialogue is valueless and (it) is necessary for us to exercise pressure."
Mr Pence said his country's longstanding alliance with Japan formed the "cornerstone" of peace in Northeast Asia.
"The alliance between the United States and Japan is the cornerstone of peace and security in Northeast Asia," he told Mr Abe.
Mr Pence will also kick off economic talks with Taro Aso, the Japanese finance minister. He then travels from Tokyo to Jakarta and Sydney.
Speaking at a news conference at the UN on Monday, North Korea's permanent representative Ambassador Kim In-ryong condemned the US missile strikes in Syria.
He said the US was "disturbing global peace and stability and insisting on gangster-like logic".
North Korea's KCNA news agency on Monday published a letter from the country’s leader, Kim Jong-un to Syrian President Bashar al-Assad, marking the 70th anniversary of Syria’s independence.
"I express again a strong support and alliance to the Syrian government and its people for its work of justice, condemning the United States’ recent violent invasive act against your country," said Mr Kim.