North Korea's apparent underground nuclear test has earned the condemnation of leaders around the world.
President Bush said that any such test by Pyongyang would constitute a threat to international peace and security. He said the leaders of China, South Korea, Russia and Japan agree that the reported action deserves an immediate response by the United Nations Security Council.
Mr. Bush also said that if Pyongyang transfers nuclear weapons or materials to anyone else, it will be held "fully accountable for the consequences."
The Chinese government called the apparent test "brazen," and urged Pyongyang to return to stalled six-party nuclear disarmament talks. China is one of North Korea's few allies and has previously responded to its neighbor's nuclear threats in measured tones.
Beijing's U.N. ambassador (Wang Guangya) said the "door is still open" for a diplomatic solution.
In Washington, a White House spokesman dismissed the possibility of one-on-one talks with Pyongyang.
South Korean officials said they would react "strictly" to the test, in line with Seoul's position that a nuclear-armed North Korea is unacceptable.
Japan quickly set up a task force to deal with what it called a threat to regional stability. Japanese Prime Minister Shinzo Abe is in Seoul for talks with South Korean President Roh Moo-hyun, mainly to discuss the nuclear issue.
Other countries with nuclear weapons were quick to denounce the development.
India said the reported test violates international commitments, adding that the claim of testing "highlights the dangers of clandestine proliferation."
Pakistan also expressed concern, calling it a "destabilizing development for the region." A Foreign Ministry spokeswoman (Tasneem Aslam) said there is no link between North Korea's apparent nuclear progress and the father of Pakistan's nuclear program, A. Q. Khan. Khan has been condemned for spreading nuclear know-how to what the United States and others consider unstable states.
And Russian President Vladimir Putin also condemned the apparent nuclear test. He said North Korea's action would cause huge damage to the process of stopping the spread of weapons of mass destruction. The Kremlin said it was also urging a coordinated international response to the development.
Britain, France, Germany, the European Union, Indonesia, Bangladesh and Australia also voiced concern.