"We'll be conducting more missile tests on a weekly, monthly and yearly basis," Vice Foreign Minister Han Song-Ryol said.
And he said an "all out war" would result if the US took military action.
Earlier, US Vice-President Mike Pence warned North Korea not to test the US.
He said his country's "era of strategic patience" with North Korea was over.
Mr Pence arrived in Seoul on Sunday, hours after North Korea carried out a failed missile launch.
Tensions have been escalating on the peninsula, with heated rhetoric from both North Korea and the US.
Speaking alongside South Korea's acting President Hwang Kyo-ahn, Mr Pence said North Korea should not test US 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," Mr Pence said.
"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 percent."
Photo: AFP / KCNA via KNS (This file photo, of what North Korea said was a missile test, was released last month).