Washington: Recent satellite photos show North Korea could be almost ready to carry out its threat to conduct a nuclear test, a US research institute said on Friday.

The images of the Punggye-ri site where nuclear tests were conducted in 2006 and 2009 reveal that over the past month roads have been kept clear of snow and that North Koreans may have been sealing the tunnel into a mountainside where a nuclear device would be detonated.

But it remains difficult to discern North Korea’s true intentions as a test would be conducted underground.

The analysis was provided to an international news agency by 38 North, the website of US-Korea Institute at Johns Hopkins School of Advanced International Studies. The latest image was taken Wednesday.

North Korea’s powerful National Defense Commission declared its plans yesterday after the UN Security Council tightened sanctions in response to a December long-range rocket launch. It described it as part of a “new phase” of combat with the United States, which retains 28,000 troops in South Korea and which it blames for leading the UN Bid to punish Pyongyang.

The North said a nuclear test was part of “upcoming” action but did not say exactly when or where it would take place.

38 North concludes that the Punggye-ri site, in the country’s northeast, “appears to continue to be at a state of readiness that would allow the North to move forward with a test in a few weeks or less once the leadership in Pyongyang gives the order.”

South Korean media have cited intelligence officials as saying technical preparations appear complete and the North could be ready to test within days of making a decision to do so.

US officials confirmed today that trucks have been moving around the site. One official said the US is not ruling out that the test could happen in the near future.

But the officials cautioned that, as in previous tests, because it would be done underground, the US may not know much before it actually happens. Officials spoke on condition of anonymity because they were not authorized to discuss intelligence matters publicly.

In 2006, North Korea detonated a nuclear device just six days after it announced its plans to do so, and in 2009, 26 days after the announcement. Both tests came weeks after the UN Security Council had condemned it for long-range rocket launches.

“While the test site appears to continue to be at a high state of readiness, it’s anyone’s guess when a detonation might occur. The North Koreans may do it tomorrow, some other day or they may decide to wait until a meaningful date like Kim Jong Il’s birthday on February 16th,” said Joel Wit, a former US State Department official and the editor of 38 North.