A week after President Trump and North Korean leader Kim Jong Un met in Hanoi, the negotiating process appears more fragile than ever. (Evan Vucci/AP)

When President Trump abruptly walked away last week from a summit with North Korean leader Kim Jong Un in Hanoi, he emphasized that it was not an angry walk, “it was a very friendly walk,” and he hoped the two sides would return to the negotiating table “soon.”

One week later, however, the negotiating process appears more fragile than ever following reports that North Korea has begun rebuilding a satellite rocket launchpad and engine test site it previously said it was dismantling.

Analysts said the move demonstrates the volatility of a negotiating process that started with Trump’s threats of North Korea’s total destruction, followed by a pair of cordial and historic summits between the two leaders, and may now enter a third phase of renewed saber-rattling.

“This is a risky move, but we know the North Koreans have a high tolerance for risk,” said Sue Mi Terry, a former senior Korea analyst at the CIA.

The message the North Korean leader is trying to send by restarting construction at the Sohae Satellite Launching Station is unclear.

The work began between Feb. 16 and March 2, according to satellite imagery published Tuesday, meaning it started just before or immediately after the breakdown of talks in Vietnam’s capital on Feb. 28.

Pyongyang had begun dismantling the station over the summer, after Kim’s first meeting with Trump in Singapore, which was taken as a positive sign of North Korea’s interest in denuclearization. The site had been used to test the engines of long-range ballistic missiles, which the United States wants to see dismantled.

During talks between North and South Korea in September, Kim offered to destroy the facility in the presence of American observers, so any construction at the site would appear to be a worrying setback for the trajectory of the talks.

Trump said Wednesday that he would be “very disappointed” if North Korea had restarted construction, but refrained from harsher criticism, calling the reports “very early.”

The State Department declined to comment, saying it does not discuss “matters of intelligence.”

North Korea has yet to comment on the reports.

South Korean intelligence officials offered two potential explanations for the construction to lawmakers in Seoul on Tuesday, according to South Korean media reports. Pyongyang may have been rebuilding parts of the site so that its dismantlement appeared to be more dramatic in the event that Kim struck a deal with Trump in Hanoi. The other possibility is that North Korea was preparing for more rocket tests in the event of a breakdown of the Hanoi talks, South Korea’s intelligence officials said.

“It’s hard to say if this is in reaction to the Hanoi summit, but in the grand scheme of things, it just confirms yet again the need for a real nuclear deal,” said Duyeon Kim, a Korea expert at the Center for a New American Security. “In Pyongyang’s view, there’s no agreement with Washington in place that prohibits or limits conducting nuclear and missile business as usual.”

Terry, a scholar at the Center for Strategic and International Studies, said the construction is almost certainly a pressure tactic Kim is using against Washington and Seoul.

“It indicates that he still thinks he can pressure the Trump administration into concluding a deal that is favorable to Pyongyang,” she said. “By threatening to reverse a commitment agreed under the Pyongyang Declaration, Kim is also simultaneously sending a message” to South Korean President Moon Jae-in that he must act quickly to “mediate between Trump and Kim or act unilaterally to move inter-Korea relations forward.”

Though Trump withheld judgment on the construction, national security adviser John Bolton took a much more aggressive posture Tuesday night, raising the prospect of tougher U.S. sanctions on North Korea.

Bolton told Fox News that if the North Koreans do not denuclearize, “they’re not going to get relief from the crushing economic sanctions that have been imposed on them and we’ll look at ramping up those sanctions up, in fact.”

That threat already marks a dramatic departure from Trump’s warm rhetoric during and after the summit, in which he called Kim his “friend.”

“There’s a warmth that we have, and I hope that stays. I think it will,” Trump said at a post-summit news conference. “You know, we’re positioned to do something very special.”

With Bolton’s threat of new sanctions, the positive atmosphere is likely to evaporate, raising the possibility of renewed saber-rattling.

During the meetings in Hanoi, Kim asked for the punishing sanctions imposed in United Nations Security Council resolutions to be lifted in exchange for the dismantling of its Yongbyon nuclear compound and other facilities.

Trump rejected the offer because he said it would have taken away the most potent sanctions against North Korea while leaving covert enrichment facilities, missiles and warheads in the country, he said.

With no clear way out of the impasse, analysts worry the two sides might resume the belligerent rhetoric they traded during Trump’s early days in office.

“This is a reminder of how we could very quickly go from serious negotiations about denuclearization and peace back to dangerous and irresponsible talk of fire and fury,” said Daryl Kimball, the executive director of the Arms Control Association.