While South Korea's military made public some sensitive intelligence on North Korea's activity at its nuclear test site, the U.S. government maintained a cautious approach, at least outwardly.
Speaking formally to reporters, U.S. officials did not rule out the possibility of another nuclear test by the unpredictable communist regime.
But they would not reveal specific information.
"North Korea has a history of taking provocative action and we are always mindful of the possibility that such an action could be taken," White House spokesman Jay Carney told reporters aboard Air Force One as President Barack Obama left for a weeklong trip to Asia, according to a transcript from the White House.
Carney added, "I would note that there is a kind of cyclical nature to the provocative actions that North Korea tends to take, and we'll be watching it very closely."
Obama is scheduled to visit Japan, South Korea, Malaysia and the Philippines.
Should the North press ahead with a nuclear test, Carney pointed out, it would represent a clear violation of its international obligations.
South Korea's defense ministry earlier announced that "a lot of activity," including increased vehicle movement, has been spotted in the Punggye-ri site in the North's remote northeastern area, where Pyongyang conducted three known underground nuclear tests -- in 2006, 2009 and 2012.
The Pentagon said it's aware of related reports from Seoul.
Pentagon Press Secretary Rear Adm. Michael Kirby described it as an "alleged pending nuclear test."
"I have nothing to announce or confirm here today," he said at a press briefing. "That aside, we continue to call on North Korea to meet its obligations, its international obligations and to stop provocative actions, whatever they are, that only further destabilize the situation on the peninsula."
As to the source of the South Korean ministry's statement on Punggye-ri, Kirby said, "I am not aware of anything they've shared specifically with the United States military. That said, I mean, there could be something through state channels."
The State Department just said it saw the press reports "regarding possible increased activity in North Korea's nuclear test site."
"We're closely monitoring the situation on the Korean Peninsula," said Jen Psaki, the department's spokeswoman.
Some South Korea media raise the likelihood of a nuclear detonation around Obama's trip to Seoul slated for Thursday and Friday.
But an analysis based on commercial satellite photos indicated that a North Korean nuclear test is not imminent.
"That may be possible but appears unlikely based on the limited commercial satellite imagery available and observations of past North Korean nuclear tests," read a report by 38 North, a U.S. website specializing in North Korea issues. "Recent operations at Punggye-ri have not reached the high level of intensity -- in terms of vehicle, personnel and equipment movement -- that occurred in the weeks prior to past detonations." (Yonhap)