Japan and the United States are stepping up efforts to dissuade North Korea from carrying out a nuclear weapons test.

Japan's chief cabinet secretary, Yasuhisa Shiozaki, said Thursday the United Nations Security Council is working on sending a strong message to North Korea, after Pyongyang said it would test a nuclear device at an unspecified date to bolster its defenses against the United States.

Washington's top envoy on North Korea, U.S. Assistant Secretary of State Christopher Hill, said in an interview on CNN Thursday that he has expressed to North Korea - through diplomatic channels - that a nuclear test would be a very bad idea.

Sergei Lavrov

Russian Foreign Minister Sergei Lavrov also told reporters Thursday that Moscow is holding direct talks with North Korea in an effort to defuse the situation.

Meanwhile, Japanese media reports say a U.S. military plane capable of detecting radiation left the U.S. airbase at Okinawa earlier Thursday headed for the Korean peninsula.

The U.S. ambassador to the United Nations, John Bolton, says France and Britain support issuing a strong statement. But he said it is not clear what China and Russia will do. They are Pyongyang's closest allies on the Security Council.

A pro-North Korean newspaper published in Japan, Choson Sinbo, said Thursday Pyongyang's plan to test a nuclear weapon is not a bluff. The paper said North Korea's proposed nuclear tests are not avoidable unless Washington settles what it calls "hostile relations" with Pyongyang.