"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.