North Korea has resumed activity at a nuclear site following its internationally condemned bomb test, a US think tank said Wednesday, amid fears that the regime will carry out more explosions.

Examining satellite photos, the US-Korea Institute at Johns Hopkins University detected a rise in traffic at the Punggye-ri site but cautioned that there was not enough evidence to assert that a new test was in the works.

The think tank said that there had been no sign of vehicles or people moving at the site for a day after North Korea carried out its third nuclear test on February 12 but that activity had resumed by February 15.

Writing on the institute's 38 North blog, analysts Jack Liu and Nick Hansen said the change over a few days may indicate that North Korea "took safety precautions to ensure radioactivity levels were sufficiently low before sending personnel back into the area."

North Korea is believed to have tightly sealed the site, making it difficult for the United States and other nations to detect from the air whether Pyongyang used uranium -- which would prove it has a second nuclear method in addition to its plutonium program.

But the analysts found activity in two different parts of the site. They said that if North Korea detonated the bomb in a tunnel in the northern area, "then the southern tunnel would be readily available for a fourth test."

North Korea likely used the northern tunnel area for its previous nuclear test in 2009, but it is not known in which area it carried out its latest explosion.

The analysts said that another reason why activity appeared to increase this month was the melting of snow that fell the day after the nuclear test.

Despite widespread international condemnation, North Korea has taken on a defiant tone since its latest nuclear test, leading to fears that it will conduct another blast or long-range rocket test.

N. Korea envoy warns S. Korea of 'final destruction'
Geneva (AFP) Feb 19, 2013 - South Korea faces "final destruction" if Seoul and its allies continue to push for tougher UN resolutions against North Korea's nuclear programme, Pyongyang warned Tuesday.

"We have never recognised the propagandist resolutions on sanctions by the UN Security Council," North Korean envoy Jon Yong Ryong told a session of the UN Conference on Disarmament.

"As the saying goes, 'a newborn puppy knows no fear of a tiger.' South Korea's erratic behaviour could only herald its final destruction," he insisted.

North and South Korea traditionally trade barbs at the UN forum -- which meets regularly in Geneva and focusses on a raft of global arms-control issues.

But in the wake of North Korea's latest nuclear test last week and a global outpouring of condemnation, the rhetoric was unusually high-pitched Tuesday.

South Korea's ambassador, Kwon Haeryong, hit back.

He said that Pyongyang's secretive regime would do better to ensure a better life for its people, in a country which has suffered intermittent famines in the past two decades.

"Everybody knows that North Korea is committing enormous resources to developing nuclear weapons and a missile capability. But it is very regrettable that a chronic food shortage persists and continually threatens people," Kwon said.

"Those Korean people are in a dire situation because of the bad allocation of their resources. The North Korean regime has continued to ask for humanitarian assistance from the international community. Considering this, we urge North Korea to focus on improving the living conditions for its entire people," he said.

Last week's test was North Korea's most powerful to date, with Pyongyang claiming a breakthrough with a "miniaturised" device.

North Korea's secretive regime repeatedly has rejected international calls to halt its nuclear programme, belittling international sanctions.

Jon also slammed the United States, blaming the superpower for the current stand-off with his country -- known officially as the Democratic People's Republic of Korea, or DPRK.

"The DPRK nuclear test is just a measure for self-defence, to cope with intensified US nuclear blackmail against it," he said.

"It is the disposition and firm will of the army and people of the DPRK to counter a high-handed policy with the toughest policy and react to pressure and sanctions with an all-out counter action," he added.

"The DPRK does not make any empty talk. It will take the toughest measure against foreign aggressors and violation of sovereignty in the future," he insisted.

The US ambassador, Laura Kennedy, said North Korea's remarks would be "offensive and unacceptable" in any setting, let alone at a conference dedicated to disarmament.

N. Korea envoy warns S. Korea of 'final destruction'
Geneva (AFP) Feb 19, 2013 - South Korea faces "final destruction" if Seoul and its allies continue to push for tougher UN resolutions against North Korea's nuclear programme, Pyongyang warned Tuesday.

"We have never recognised the propagandist resolutions on sanctions by the UN Security Council," North Korean envoy Jon Yong Ryong told a session of the UN Conference on Disarmament.

"As the saying goes, 'a newborn puppy knows no fear of a tiger.' South Korea's erratic behaviour could only herald its final destruction," he insisted.

North and South Korea traditionally trade barbs at the UN forum -- which meets regularly in Geneva and focusses on a raft of global arms-control issues.

But in the wake of North Korea's latest nuclear test last week and a global outpouring of condemnation, the rhetoric was unusually high-pitched Tuesday.

South Korea's ambassador, Kwon Haeryong, hit back.

He said that Pyongyang's secretive regime would do better to ensure a better life for its people, in a country which has suffered intermittent famines in the past two decades.

"Everybody knows that North Korea is committing enormous resources to developing nuclear weapons and a missile capability. But it is very regrettable that a chronic food shortage persists and continually threatens people," Kwon said.

"Those Korean people are in a dire situation because of the bad allocation of their resources. The North Korean regime has continued to ask for humanitarian assistance from the international community. Considering this, we urge North Korea to focus on improving the living conditions for its entire people," he said.

Last week's test was North Korea's most powerful to date, with Pyongyang claiming a breakthrough with a "miniaturised" device.

North Korea's secretive regime repeatedly has rejected international calls to halt its nuclear programme, belittling international sanctions.

Jon also slammed the United States, blaming the superpower for the current stand-off with his country -- known officially as the Democratic People's Republic of Korea, or DPRK.

"The DPRK nuclear test is just a measure for self-defence, to cope with intensified US nuclear blackmail against it," he said.

"It is the disposition and firm will of the army and people of the DPRK to counter a high-handed policy with the toughest policy and react to pressure and sanctions with an all-out counter action," he added.

"The DPRK does not make any empty talk. It will take the toughest measure against foreign aggressors and violation of sovereignty in the future," he insisted.

The US ambassador, Laura Kennedy, said North Korea's remarks would be "offensive and unacceptable" in any setting, let alone at a conference dedicated to disarmament.