SEOUL: North Korea threatened on Wednesday to conduct a second nuclear test and to test-launch ballistic missiles unless the United Nations Security Council apologises for condemning its recent rocket launch.

"Unless the UN Security Council offers an apology immediately, we will be forced to take additional self-defence measures to protect the highest interests of our republic," a foreign ministry spokesman said in a statement carried by the official Korean Central News Agency.

"They will include a nuclear test and ballistic missile tests," the statement said.

The Security Council had condemned the North's April 5 launch of a long-range rocket and ordered tougher enforcement of existing sanctions.

The communist state reacted angrily then, insisting that the launch -- widely seen as a disguised missile test -- was conducted to put a peaceful satellite into orbit.

The statement on Wednesday is the latest in a string of bellicose proclamations by communist North Korea since the rocket launch and the widespread international condemnation that followed.

On April 14, Pyongyang announced it was quitting six-nation nuclear disarmament talks and restarting the programme which produced weapons-grade plutonium.

Last Saturday it said work had already begun to reprocess thousands of spent nuclear fuel rods, hours after the UN decided to freeze the foreign assets of three North Korean firms suspected of aiding the missile programme.

The North tested an atomic weapon in October 2006 but just over four months later it signed a landmark six-nation deal to disable its atomic plants in return for energy aid and other concessions.

Progress on the pact -- which the North has now abandoned -- was stalled by disagreement over how to verify the North's declared nuclear activities.

The foreign ministry demanded that the 15-member council immediately apologise for "infringing" the country's sovereignty and retract "all its resolutions and decisions" against Pyongyang.

It also announced plans to build a light-water nuclear reactor and said it would immediately start developing technology to produce fuel for it.

The ministry denounced the Security Council for "illegal and reckless acts of provocation" by sanctioning the three firms.

Such sanctions would not work, it asserted, because North Koreans have lived under those measures for many years, adding the Korean peninsula was now "on the brink of war".