Donald Trump is open to another summit with Kim Jong-un, the White House said, despite evidence that North Korea has completed reconstruction work on a rocket launch site since the two leaders’ inconclusive meeting in Hanoi last week.

John Bolton, Trump’s national security adviser, repeated the president’s comments, saying it would be “very, very disappointing” if the North Korean regime was reversing the confidence-building gestures it made last year, dismantling a space launch pad and a nuclear test site.

But Bolton told Fox News that the president was “still open to talking again”.

Asked for his reaction to developments in North Korea since Hanoi, Trump himself replied cryptically: “We’ll let you know in about a year.”

New satellite imagery published on Thursday suggested that the Sohae space launch site was fully operational once more. Although it has so far been used only for putting satellites into space, the launch vehicles use some of the same technology as intercontinental ballistic missiles (ICBMs).

Adding to the tension, new activity has been reported at a North Korean plant that makes ICBMs and space launch rockets.

“The fact that both facilities are active at the same time suggests that there are preparations for a new launch, but it is impossible to tell what they are going to launch,” said Melissa Hanham, a North Korea expert at the One Earth Future foundation.

Grace Liu, a research associate at the Middlebury Institute of International Studies at Monterey, said: “Everything we have seen is consistent with a space vehicle launch.” But Liu added that the North Koreans could install powerful new ICBM engines into their space launch vehicle if they wanted to launch a heavier satellite.

That would deepen the dispute over whether a satellite launch breached Kim’s undertaking to Trump to continue his moratorium on missile launches, and whether it violated a UN security council resolution on missile testing.

The news of possible new missile activity follows the failure of the Hanoi summit a week ago, and was further sign that the progress made last year by Trump and Kim towards defusing tensions, may be starting to unravel. The president has pointed to the absence of nuclear or missile tests since late 2017 as the main achievement of his diplomatic initiative.

Bolton was noncommittal about the significance of the evidence of new missile work.

“I don’t think we really are in a position to say at this stage,” he told Fox News. “Obviously we have a lot of ways of getting information. We’re going to study the situation carefully. As the president said, it would be very, very disappointing if they were taking this direction.”

But the national security adviser added that Trump was still ready to do a “big deal” trading North Korean denuclearisation for sanctions relief.

“The president’s obviously open to talking again. We’ll see when that might be scheduled or how it would work out,” Bolton said.

A North Korea research site, 38 North, published satellite images taken on Wednesday that it said showed reconstruction work at the Sohae satellite launching facility appeared to have been completed, with cranes having been removed from the site.

“Given that construction plus activity at other areas of the site, Sohae appears to have returned to normal operational status,” the website reported.

However, 38 North’s director, Joel Wit, said the repair work did not necessarily mean a test launch was imminent, and if there was a launch it was unlikely to be an ICBM.

“Of all different scenarios, the least likely is a full ICBM test, because they don’t need to test from this site,” Wit said. “Why would they do it from a fixed launcher that everyone is watching?”

North Korea’s two previous ICBM tests have been made from mobile launchers. But Wit warned that a space launch vehicle could be tested at Sohae that used ICBM components which that could advance the regime’s grasp on long-range missiles technology.

“They would claim that they were testing a space launch vehicle which the missile test moratorium does not cover, which would also give them plausible deniability with Russia and China,” he said. “But it would put pressure on the Americans, and show is just as tough as Donald Trump.”