WASHINGTON (AFP/Reuters) - North Koreas nuclear bomb test drew stern rebukes Monday from global leaders with Barack Obama warning of grave danger and Israel highlighting negative implications in the Middle East. South Korea put its military on alert and world powers frustrated by failed diplomatic efforts to rein in Pyongyang demanded a firm response ahead of a UN Security Council emergency meeting later Monday in New York. Even China, the secretive Norths closest international ally, expressed resolute opposition. The North Korean explosion an underground blast the size of a mid-sized earthquake, according to seismologists was a much bigger follow-up to its first nuclear test in 2006. It came amid reports that Pyongyang also tested a short-range missile. North Koreas nuclear ballistic missile programs pose a grave threat to the peace and security of the world and I strongly condemn their reckless actions, Obama said in a statement. The president called the testing a blatant violation of international law as well as its own public position, saying North Korea had chosen to ignore its previous commitment to abandoning its nuclear program. Obama said North Korea had flauted United Nations resolutions, with the result it is not only deepening its own isolation, its also inviting stronger international pressure. Thats evident overnight as Russia, China, as well as our traditional allies of South Korea and Japan have all come to the same conclusion: North Korea will not find security and respect through its threats and illegal weapons. Nuclear-armed Israel and the United States suspect Iran of trying to develop atomic weapons, a charge Tehran has repeatedly denied. Israels foreign ministry was clearly referring to its greatest enemy when it said in a statement that North Koreas nuclear proliferation... has negative implications in this region. It demanded that the UN react with an unambiguous message to other countries. South Koreas President Lee Myung-Bak chaired a special national security council meeting while Japanese Prime Minister Taro Aso said the testing raises tensions in the region extremely. UN Secretary-General Ban Ki-moon, himself South Korean, said he was deeply disturbed. The main powers on the council all strongly condemned North Korea with France urging sanctions against Kim Jong-Ils Stalinist administration, as foreign ministers from Asia and Europe began two days of talks. China strongly demands that North Korea keeps its promise of denuclearisation and ceases all actions that could further worsen the situation, the Chinese foreign ministry said in its statement. Russia, which has sought a role in efforts to end North Koreas nuclear weapons programme, said the test would provoke an escalation of tensions in northeast Asia, according to a foreign ministry statement. British Prime Minister Gordon Brown said the test was a danger to the world, while South Africa warned the possession of nuclear weapons constitutes a threat to all humanity. In Brussels, the NATO military alliance said the provocative test was a serious challenge to peace. South Korea, Russia, China, the United States and United Nations have sought to engage the North in so-called six-party talks on its nuclear programme. But a 2007 accord broke down with the Norths test-firing of a long range missile in April. North Korea angrily reactivated its nuclear programme after being condemned by the UN Security Council for that action. John Bolton, a US ambassador to the United Nations under former president George W. Bush, said Obama now faces a moment of truth and suggested it was time to expel North Korea from the UN. Speaking on Fox News television, he said Obamas special envoy, Stephen Bosworth, had recently given North Korea a signal that they could get away with it. Bolton also warned of Middle East repercussions, given the cooperation between North Korea and Iran on ballistic missiles. Experts have accused North Korea of using the test blast as a means to secure international concessions. They have serious economic problems, they struggle to feed their people... They are clearly engaged in a cynical game where they are using nuclear technology to gain economic and energy advantages, said Norways Foreign Minister Jonas Gahr Stoere. US Secretary of State Hillary Clinton on Monday told Japan and South Korea that she wanted a strong, unified approach to the nuclear threat posed by North Korea, her spokesman Ian Kelly said. Secretary Clinton is engaged in intensive diplomacy concerning the DPRKs claims of a nuclear test, Kelly said in a statement, referring to the acronym for North Korea. UN-backed international committee preparing a nuclear test ban treaty said Monday that North Koreas announcement that it carried out a nuclear test should be universally condemned. Todays nuclear test claimed by the Democratic Peoples Republic of Korea (DPRK) constitutes a threat to international peace and security and to the nuclear non-proliferation and disarmament regime, Tibor Toth, executive secretary of the preparatory committee for the Comprehensive Nuclear Test Ban Treaty Organisation said in a statement. I am gravely concerned by this action. In particular, it is a serious violation of the norm established by the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and as such deserves universal condemnation. The North Korean move underlines the urgency of the entry into force of the CTBT and the necessity of putting an end to all nuclear explosions for all time, Toth continued. It is therefore my hope that the current situation will increase political momentum towards the CTBTs entry into force and speed up the ratification process.