North Korea successfully conducted its first nuclear test on Monday, ignoring international warnings and risking economic sanctions, according to the North's official Korean Central News Agency.

Nations worldwide condemned the test with the United States and South Korea calling it a 'provocative act' and China stating that it 'resolutely opposed' the nuclear test that North Korea 'flagrantly conducted' to universal opposition.        

The underground test was conducted 'successfully' and 'safely' with no leaks of radioactivity, according to KCNA. South Korea, the US and Russia [Images] confirmed a seismic tremor between 3.6 and 4.2 on Richter scale at 07:06 am (0136 GMT).

The power of the blast has not been officially confirmed, but the state-run Korea Institute of Geoscience and Mineral Resources said it was small, equivalent to around 550 tons of TNT explosives.

Though North Korea announced it will conduct the test last Tuesday, accusing the US of being hostile and trying to isolate it, no timeline was given.

Japan [Images], South Korea and the United States have agreed to work closely in protest against North Korea's nuclear test, Japanese Foreign Minister Taro Aso said, adding that it is a 'considerable threat to the peace and stability of northeast Asia and the world.'

"North Korea's action can only lead to an intensification of the problems on the Korean Peninsula, threaten world peace and stability in the region and undermine nuclear non-proliferation," Russian Foreign Ministry spokesman Mikhail Kamynin said.

North Korea should take immediate steps to comply with the Nuclear Non-Proliferation Treaty and resume stalled six-way talks with South Korea, China, Japan, Russia and the United States, he added.

The KCNA said the test, 'will contribute to defending the peace and stability on the Korean Peninsula and in the area around it.' South Korea's military has increased the number of troops near land and sea borders.

However the alert level has not been raised beyond usual defence situations, the Joint Chiefs of Staff said, adding that no unusual military movement has been detected in North Korea.

Meanwhile, the White House has called on the United Nations Security Council 'to act immediately' to North Korea's unprovoked action.

The UN Security Council had said on Friday that any nuclear test by North Korea will amount to a threat to world peace and security, and that the Security Council will 'act consistent with its responsibility under the Charter of the United Nations.'

The Security Council is likely to meet o Monday and push for a resolution condemning North Korea and impose a number of stringent economic sanctions. South Korea has already suspended a scheduled shipment of emergency relief aid to North Korea, the Unification Ministry said.

The timing of the test coincides with Japanese Prime Minister Shinzo Abe's [Images] arrival in Seoul from Beijing [Images]. "North Korea's nuclear test will never be pardonable," he said during a lunch meeting with South Korean Prime Minister Han Myeong Sook.

On Sunday, China and Japan had agreed that they could 'never tolerate' a nuclear test by North Korea. According to analysts, Pyongyang is trying to force the US into bilateral talks, ending all attempts by the stalled six-party talks.

- DPA