The U.S. says it is keeping close watch on movements in the North amid speculation that it may carry out a fourth nuclear test while U.S. President Barack Obama is visiting the region over the next week.
Speaking to reporters on Air Force One, White House Spokesman Jay Carney said the U.S. is monitoring movements at the North's Punggye-ri nuclear test site.
South Korea's defense ministry had earlier reported detecting increased activity there.
The U.S. State Department echoed Carney's sentiment and urged North Korea to exercise restraint.
"We continue to urge North Korea to refrain form actions that threaten regional peace and security to comply with international obligation and committment"
The U.S.-based North Korea analysis site, 38 North, does not believe the regime will carry out a fourth nuclear test while President Obama is in the region.
It said the recent activities detected in satellite imagery of the Punggye-ri nuclear test site are dissimilar to those seen in the weeks before previous detonations, and do not suggest a test is imminent.
Shin Se-min, Arirang News.