North Korea vowed on Sunday to push ahead with what it says are peaceful nuclear and space programmes, rubbishing calls from the five permanent UN Security Council members.
The communist North condemned a statement issued Thursday by the United States, ally China, Russia, France and Britain on the sidelines of a non-proliferation meeting in Vienna.
They had expressed "serious concern" and urged Pyongyang to "refrain from further actions which may cause grave security concerns in the region, including any nuclear tests".
There has been widespread speculation the North could stage its third nuclear test following a failed rocket launch on April 13 that sparked international criticism.
A South Korean nuclear expert had said that the North has finished preparations for a third nuclear test, while satellite photos of the North's Punggye-ri test site show work in progress.
Thursday's statement was an "illegal act that infringes upon" the North's right to use space and nuclear power for peaceful purposes, an unnamed North Korean foreign ministry spokesman said through state media.
"We will... persistently safeguard the sovereignty of our nation, based on self-defensive nuclear deterrent, and strongly pursue our peaceful space development and the development of our nuclear power industry," the spokesman said.
US Secretary of State Hillary Clinton said Friday in Beijing that Washington was ready to work with Pyongyang if it changed course, but she voiced doubts about the regime's intentions.