United Nations - The U.N. Security Council swiftly condemned North Korea's nuclear test on Monday as "a clear violation" of a 2006 resolution banning them and said it will start work immediately on a new one that could result in stronger measures against the reclusive nation.

    Hours after North Korea defiantly conducted its second test, its closest allies China and Russia joined Western powers and representatives from the rest of the world on the council to voice strong opposition to the underground explosion.

    After a brief emergency meeting held at Japan's request, the council demanded that North Korea abide by two previous resolutions, which among other things called for Pyongyang to return to six-party talks aimed at eliminating its nuclear program. It also called on all other U.N. member states to abide by sanctions imposed on the North.

    Russia's U.N. Ambassador Vitaly Churkin, the current council president, made clear in a statement that the condemnation was only an initial response, and that more will follow. He said it was too early to give any specifics.

    "The members of the Security Council have decided to start work immediately on a Security Council resolution on this matter," he said.

    U.S. Ambassador Susan Rice said the 15-member council agreed that work on the new resolution will begin Tuesday.

    "What we heard today was swift, clear, unequivocal condemnation and opposition to what occurred," she said. "The United States thinks that this is a grave violation of international law and a threat to regional and international peace and security and therefore the United States will seek a strong resolution with strong measures."

    Churkin was asked whether Russia viewed the nuclear test as more serious than North Korea's missile launch in April, which also led to Security Council condemnation and sanctions against three North Korean companies.

    "This is a very rare occurrence as you know, and it goes contrary not only to resolutions of the Security Council but also the (Nuclear) Nonproliferation Treaty and the (Nuclear) Test Ban Treaty," he replied. "We are one of the founding fathers - Russia is - of those documents, so we think they're extremely important in current international relations. So anything which would undermine the regimes of those two treaties is very serious and needs to have a strong response."

    The five permanent veto-wielding members of the council - the United States, Russia, China, Britain and France - met behind closed doors for over an hour with the ambassadors of Japan and South Korea ahead of the closed meeting of the full 15-member council.

    Japan said North Korea's "irresponsible" nuclear test and the April missile launch had challenged the authority of the U.N.'s most powerful body "and the response must be firm."

    "It's a very clear challenge," said Japan's U.N. Ambassador Yukio Takasu, a non-permanent council member. "So therefore we need a really, really clear and firm message from this - preferably a resolution."