TOKYO — Satellite images suggest that North Korea was preparing to launch a space rocket even before the breakdown of the Hanoi summit between President Trump and Kim Jong Un, experts say.

There is no way to know whether Pyongyang will follow through with the plans, which would undoubtedly be viewed negatively in Washington and could derail an already shaky negotiation process. Meanwhile, signs of a hardening of attitudes within the Trump administration have left several experts increasingly pessimistic.

The plans may reflect a feeling that talks had already hit an impasse even before the summit, as well as North Korea’s frustration about a lack of sanctions relief, experts say. Kim, the North Korean leader, had already warned in a New Year’s Day speech that he might be forced to follow a “new path” if the United States demanded unilateral concessions and did not lift sanctions.

The images showed signs of activity on Feb. 22 at the Second Academy of Natural Sciences at Sanumdong, just outside Pyongyang, which is North Korea’s primary developer of ballistic missiles and space launch vehicles.

Other images made available this week show that North Korea has also rebuilt a launchpad and rocket engine test site at the Sohae Satellite Launching Station, reinforcing suspicions that a rocket launch could be imminent.

In 2012, an agreement between North Korea and the Obama administration to cease nuclear and missile tests in return for food aid broke down after Pyongyang launched a satellite rocket. Trump has set considerable store in a promise by Kim to suspend testing and said Friday that he would be “very disappointed” if testing resumed.

“With the inconclusive result in Hanoi, North Korea now appears to be moving again toward a space launch,” Jeffrey Lewis, a scholar at the Middlebury Institute of International Studies at Monterey, in California, wrote in a blog post.

Lewis said he expected that North Korea would use older, and already tested, technology for a space launch but that it could use a larger rocket that would send a more provocative signal.

“If North Korea wants to place a satellite in geostationary orbit . . . it will require a larger launch vehicle,” he wrote. “North Korea might instead debut a new rocket, possibly using a variant of the March 18 Revolution engine that powers its new generation of strategic missiles including the Hwasong-15.”

Lewis said the move followed a pattern of North Korean negotiating tactics: “Pressure before the summit to make deal, followed by a credible punishment after the U.S. walks away.”

He added: “Trump is going to lose his one foreign policy victory bit by bit.”

Attitudes also appear to be hardening in Washington. On Thursday, a senior State Department official said the launch of a space launch vehicle from Sohae “would be inconsistent with the commitments that the North Koreans have made.”

But more significant to many experts was a comment that appeared to put the ball squarely in Pyongyang’s court to dismantle its nuclear weapons before the United States would consider easing the pressure.

“So nobody in the administration advocates a step-by-step approach,” said the official, who spoke on the condition of anonymity under State Department guidelines. “In all cases, the expectation is a complete denuclearization of North Korea as a condition for all the other steps being — all the other steps being taken.”

Experts said the latest remarks appear to contradict a speech by Stephen Biegun, the U.S. envoy to North Korea, at Stanford in January, when he said he hoped the two sides could move “simultaneously and in parallel,” through a road map of “concrete deliverables,” negotiations and declarations.

Instead, the official’s comments suggest the Trump administration is losing interest in a gradualist approach built around confidence-building and reciprocal steps. Instead, it seems to be banking on Trump’s offer that Kim go “all in” and surrender its nuclear and missile arsenal in one go, in return for economic rewards and “a brighter future.” Among the North Korea-watching community, such a prospect is considered completely unrealistic.

“I can certainly affirm what the president proposed to Chairman Kim, which was the complete elimination of their weapons of mass destruction program,” the official said. “We still believe this is all achievable within the president’s first term, and that’s the timetable we’re working on.”

Meanwhile, North Korean state media has finally admitted the breakdown of the talks in Hanoi, after a week in which it declared them a success.

“The entire world is sincerely hoping for smooth process in the peace process on the Korean Peninsula and prompt improvement of the North Korea — United States relations,” Rodong Sinmun, the official newspaper of the Workers’ Party of Korea, wrote in a commentary. “People at home and abroad are regretting and lamenting over the unexpected absence of an agreement at the summit, holding the United States responsible for it.”

But the commentary said the real fault lay with Japan, a key U.S. ally that has consistently taken a more hawkish stand toward Pyongyang.

“The reactionaries in Japan are impudently cheering over the news,” it wrote. “The mean tricks that the Japanese played to disturb the Hanoi summit make us wonder how such bastards even have a place on the earth.”

Min Joo Kim in Seoul contributed to this report.