North Korea reportedly fired two short-range missiles on Tuesday, in a move set to heighten tensions after its latest nuclear weapons test drew global condemnation.

The UN Security Council held an emergency meeting to consider the options after Pyongyang's test of a nuclear device on Monday, which some estimates said was almost as powerful as the atom bombs that flattened Hiroshima and Nagasaki.

The Council called the test a "clear violation" of international law and immediately began working on a resolution that could impose new sanctions on the secretive North, which has now tested two nuclear bombs in three years.

"This resolution should include new sanctions in addition to those already adopted because such behaviour should have a cost and a price to pay," said Jean-Pierre Lacroix, the deputy French ambassador to the United Nations.

Following the UN condemnation, the North launched one ground-to-air missile and one ground-to-ship missile into the sea Tuesday off its eastern coast near the city of Hamhung, South Korea's Yonhap news agency reported.

"Intelligence authorities are analysing the motives for the firing," it wuoted a South Korean government source as saying, adding that each missile had a range of 130 kilometres (80 miles).

In April it test-fired a long-range rocket that critics say was in fact a ballistic missile, and on Monday it test-fired three short-range missiles after the nuclear blast.

Russia estimated the force of Monday's underground nuclear explosion at up to 20 kilotons, far more powerful than the October 2006 test that announced the impoverished communist state had joined the club of world nuclear powers.

The North said the latest test would "contribute to defending the sovereignty of the country and the nation and socialism, and ensuring peace and security on the Korean peninsula and the region."

North Korea has repeatedly said it needs a deterrent to ward off an attack by the United States, which it believes wants to topple Kim Jong-Il's regime. Almost six years of disarmament talks have not stopped its nuclear drive.

Some analysts have suggested that Kim is using the nuclear test to strengthen his hand at home, and so could be even less swayed than usual by more sanctions or international criticism.

The 67-year-old was widely reported to have suffered a stroke last August, prompting speculation overseas about the succession. The North's position has noticeably hardened since then.

"This is part of Kim shoring up support for his regime among the inner circle and the public," Peter Beck, a Korea expert at the American University in Washington, told AFP.

"The internal domestic dynamic is taking precedence over external factors."

Even China, a permanent member of the Security Council and the North's sole main ally, was strongly critical of the latest test -- which North Korea had pledged to carry out because of previous censure from the Council.

"Disregarding the common objections of the international community, the Democratic People's Republic of Korea has again tested a nuclear device," China's foreign ministry said in a statement.

"The Chinese government expresses its resolute opposition to this," it said.

US President Barack Obama, whose initial overtures to the North since taking office in January have been met with official hostility from Pyongyang, condemned what he called its "reckless" atomic test.

"North Korea's nuclear ballistic missile programmes pose a great threat to the peace and security of the world," he said.

The North Tuesday reiterated complaints that Obama is no better than his predecessor.

"The present US administration is talking about what it called a 'change' and 'bilateral dialogue' but it is, in actuality, pursuing the same reckless policy as followed by the former Bush administration to stifle the DPRK (North Korea) by force of arms," said the ruling party newspaper Rodong Sinmun.

Foreign ministers from Asia and Europe meeting in Hanoi were set to condemn the nuclear test as "a clear violation" of six-party agreements and UN resolutions, according to a draft text.

South Korea announced it was joining the US-led Proliferation Security Initiative, an international effort to curb trade in weapons of mass destruction that involves some 90 nations and includes military exercises.

North Korea had previously said that it would see the South's participation as a declaration of war.

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