North Korea has vowed to retaliate and make "the US pay a price" for drafting fresh UN sanctions over its banned nuclear weapons programme.
The sanctions, which were unanimously passed by the UN on Saturday, were a "violent violation of our sovereignty," the official KCNA news agency said.
Separately, South Korea says the North has rejected an offer to restart talks, dismissing it as insincere.
The sanctions will aim to reduce North Korea's export revenues by a third.
The UN Security Council decision followed repeated missile tests by the North which have escalated tensions on the peninsula.
In its first major response on Monday, North Korea insisted that it would continue to develop its controversial nuclear weapons programme.
The state-run KCNA news agency said Pyongyang would "not put our self-defensive nuclear deterrent on the negotiating table" while it faces threats from the US.
It threatened to make the US "pay the price for its crime... thousands of times," referring to America's role in drafting the UN sanctions resolution.
Speaking to reporters at a regional forum in the Philippine capital, Manila, North Korean spokesman Bang Kwang Hyuk said: "The worsening situation on the Korean peninsula, as well as the nuclear issues, were caused by the United States.
"We affirm that we'll never place our nuclear and ballistic missiles programme on the negotiating table, and won't budge an inch on strengthening nuclear armament."
The remarks come after reports emerged that the North and South Korean foreign ministers had met briefly on Sunday evening on the sidelines of the Association of Southeast Asian Nations (Asean) summit in Manila.
South Korean media reported that its Foreign Minister, Kang Kyung-wha, shook hands with her North Korean counterpart, Ri Yong Ho, in a brief and unarranged meeting at an official dinner event.
A South Korean official told the BBC that Mr Ri had dismissed Ms Kang's offer of talks as "insincere".