The US is demanding North Korea destroys all its nuclear, chemical and biological weapons before receiving any sanctions relief, as positions harden on both sides in the aftermath of last week’s failed Hanoi summit.

The US clarified its demands after satellite images showed the North Koreans had completely rebuilt a space launch site they had partially dismantled after the first summit between Donald Trump and Kim Jong-un in June last year.

The US state department said it was seeking clarification from Pyongyang on the purpose of the reconstruction work, but made it clear that any launch at the site, even to put a civilian satellite into orbit, would be a violation of Kim’s commitments to Trump.

Trump’s national security adviser, John Bolton, said the US president was open to another summit with Kim, but that the US wanted to discuss a “big deal” involving complete disarmament in return for comprehensive sanctions relief that would give North Korea a “bright future”.

South Korea’s president, Moon Jae-in, underlined his determination to prioritise inter-Korean relations when he appointed a longtime confidant as Seoul’s point man on relations with the North.

Kim Yeon-chul, a pro-engagement scholar who has headed the state-run Korea Institute for National Unification since April last year, replaced Cho Myoung-gyon as unification minister in a cabinet reshuffle announced on Friday, according to South Korean media.

In the US, a senior state department official added further clarity to the US negotiating position which had become hazy in the run-up to the ill-fated Hanoi summit, saying that a phased approach, in which some disarmament would be rewarded with a degree of sanctions relief, was not on the table.

“Nobody in the administration advocates a step-by-step approach. In all cases the expectation is the complete denuclearisation of North Korea as a condition for all the other steps being taken,” the official said, confirming that Trump had also called on Kim to get rid of all North Korea’s chemical and biological weapons at the same time.

He argued that the negotiating strategies pursued by previous US administrations had involved a phased approach and had failed.

“We’re trying to do it differently here,” he said. The official said the administration remained confident that North Korea’s complete disarmament could achieved by the end of Trump’s current presidential term.

“My personal view is that this is going to get worse before it gets better,” Victor Cha, a former director of Asian affairs at the National Security Council. “The one lesson that both sides learned from Hanoi is that each feels that pressure worked. Now they want to soften each other’s positions.”

Satellite images suggest North Korea’s rebuilding of the Sohae launch facility. Photograph: Digitalglobe Handout/EPA

Cha, now at the Centre for Strategic and International Studies, said that by demanding complete disarmament, the Trump team was “setting a very high bar for coming back to the table. Basically it’s all or nothing.”

New satellite imagery published on Thursday suggested 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.

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.

The senior state department official said that the administration had seen the rebuilding work at Sohae, but had not reached a conclusion on the intention behind it.

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?”