A U.S. research institute devoted to analysis of North Korea says the country's nuclear site is in a high state of readiness to conduct another nuclear test.
Joel Wit, the founder of 38 North website, said satellite images show that such a test could be conducted within weeks if ordered by Pyongyang.
"What we see is a lot of activity at the site and it's easy for us to see that because there has been snow there and you can see that the roads that are in use are not covered with snow, nor are a lot of the footpaths in the area near the test tunnel," he said.
Wit said that satellite photos taken on January 4 also show many North Koreans lined up near the entrance to the test tunnel which, he says, could be armed guards. In addition, there are a lot of buses and other vehicles in the area, which he says is unusual in the winter.
North Korea has threatened to conduct its third nuclear test and carry out more rocket launches in retaliation after the U.N. Security Council this week unanimously passed a resolution tightening sanctions against Pyongyang for pursuing nuclear weapons.
Wit said the U.S. North Korea policy in the past four years has not produced any results and that it needs to be re-evaluated. He said that engaging in a diplomatic effort may help.
Pyongyang also has threatened "strong physical countermeasures" against South Korea if Seoul directly takes part in the sanctions.
A statement released Friday by the North's Committee for Peaceful Reunification of the Fatherland warned that sanctions mean a declaration of war. The statement also threatened to end all dialogue with anyone on denuclearization.
Analysts say North Korea's provocative behavior is a warning to South Korea's incoming administration not to continue its current tough policy against the North.
Although the North Korean statement Thursday said the nuclear tests and rocket launches were "targeted at the United States," analysts say North Korea does not have a missile capable of reaching the U.S. mainland. They say it also has not mastered the technology necessary to mount a nuclear warhead on a long-range missile.
U.S. envoy Glyn Davies called North Korea's threats "troubling and counterproductive." Speaking in Beijing, he said his Chinese counterparts had agreed a new nuclear test would be harmful.