Satellite images taken weeks after the first Trump-Kim summit past year in Singapore had shown the North was taking steps to dismantle the rocket engine test stand and the rail-mounted transfer structure at the launch pad.
"I think it remains good", he said.
Following the stalemate in Hanoi, researchers said this week that Pyongyang had started rebuilding the Sohae long-range rocket site after Kim had agreed previous year to shut it as part of confidence-building measures. He added Thursday that he is "a little disappointed". "That's what we are working for", he said. You were going to war, folks, whether you know it or not ...
One of the experts, Jeffrey Lewis, told Reuters the activity at the two sites was "probably connected".
U.S. media had speculated over whether Trump might tighten the thumbscrews on Pyongyang following the Vietnam summit, by ratcheting up an already crippling sanctions regime. A senior State Department official told reporters on Thursday that Washington isn't considering sanctions exemptions for inter-Korean economic projects.
North Korea has frozen nuclear and missile testing since 2017, and Trump has pointed to this as a positive outcome from almost a year of high-level engagement with North Korea.
Even as Washington increasingly turns its attention toward next year's presidential election, the administration exhumed a goal that has always been buried and seen as unrealistic by experts: the total denuclearization of North Korea by the end of Mr Trump's term in 2021. Unless re-elected, Trump's term will end in January 2021.
However, a State Department official told the Wall Street Journal it was unclear why there were ongoing works being carried out at the site, and stressed the situation was being monitored.
The shake-up allows incumbent aides to run in parliamentary elections next year, analysts said, and turns a page for an administration facing a sluggish economy and sagging popularity.
Pyongyang used the site in 2012 and 2016 to launch satellites, a maneuver Western experts believe informs its development of inter-continental missiles capable of striking the United States.
Bolton, who has argued for a tough approach to North Korea, said this week that Trump was open to more talks, but also warned of tougher sanctions if North Korea did not denuclearize.
But immediately after the summit North Korean media said only that Pyongyang and Washington have agreed to continue "productive" discussions on denuclearisation.
Carter, who served as the 39th US president, visited North Korea in 1994 to meet Kim Il Sung toward facilitating negotiations with the Clinton administration at a time when tensions were high between Pyongyang and Washington.
It comes after reports earlier this week that North Korea's main rocket launch site at Sohae had been rebuilt. They called the North Korean actions "an affront to the president's diplomatic strategy" that also showed Pyongyang's "pique" over Trump's refusal to lift sanctions.
United States officials say the main goal for now is to make sure the North Koreans do not resume testing in any way, including of space launch vehicles. That is why he has thrown Kim yet another gift by scrapping joint military exercises with South Korea.