The US still believes the "fully verified denuclearization" of North Korea is possible by the end of President Donald Trump's "first term," a senior official said Thursday, according to AFP.
The statement came despite warnings that a key North Korean rocket launch site appears to have resumed operations.
The specialized website 38 North and the Center for Strategic and International Studies used commercial satellite imagery to track construction at the site, which they said began before last week's aborted summit in Hanoi between Trump and North Korean leader Kim Jong Un.
Images taken on March 6 showed that a rail-mounted structure to transfer rockets to the launching pad appeared to have been completed and "may now be operational."
Cranes have been removed from the pad, while progress also appeared to have been made on rebuilding the support structure for a rocket engine testing stand.
"Given that construction, plus activity at other areas of the site, Sohae (Satellite Launching Station) appears to have returned to normal operational status," 38 North's report said.
News of the operational site will compound the White House's frustration over the lack of progress on talks with the North.
Trump a week ago abruptly ended his summit with Kim in the capital of Vietnam, explaining that, while "we had a productive time," no deal was signed.
He said that Kim had asked for total removal of sanctions before denuclearization, something to which the US could not agree.
“Basically, they wanted the sanctions lifted in their entirety, but we couldn’t do that ... we had to walk away from it."
Trump’s move came just after Kim indicated he was ready for denuclearization, telling reporters that he would not have come to the summit in Vietnam if he was not prepared to pursue the denuclearization of the Korean peninsula.
Despite the breakdown of the summit, North Korean media later indicated that Kim and Trump had decided to continue productive talks to resolve problems discussed at their Hanoi summit.
The US official confirmed on Thursday that Washington would seek from Pyongyang "clarifications on the purposes" of rebuilding the site, adding so far the US has not reached "any specific conclusion about what's happening there."
"We're watching in real time, as you are, the developments at Sohae," he explained, adding, "We don't know why they are taking these steps."
Kim had agreed to shutter Sohae at a summit with South Korean President Moon Jae-in in Pyongyang as part of confidence-building measures, and satellite pictures in August suggested workers were dismantling the engine test stand.
Trump equivocated when asked Thursday if he was disappointed about the news. "We'll see," he said. "We'll let you know in about a year."
The president had declared that it was "too early" to tell if a previous report about activity at the site was true, but said he would be "very, very disappointed in Chairman Kim" if the intelligence checked out.