Satellite photos showing new activity at a North Korean rocket launch site have raised fresh doubts that Kim Jong-un will ever give up his drive for nuclear weapons.
But US President Donald Trump has said he is still hoping to reach an agreement on the issue that eluded the leaders at their summit last week.
The president said his relationship with the North Korean leader remains “good”, even though Mr Trump walked away from negotiations at their high-profile meeting in Vietnam.
The North Korean leader had promised in Vietnam to extend his ban on nuclear and rocket tests.
Asked about reports of new work at the Sohae Satellite Launch Station, which is tucked into the hills north-west of Pyongyang, Mr Trump said: “I would be very, very disappointed in Chairman Kim.”
Past US administrations have discovered the perils of trying to do business with North Korea, which has a history of backing out of agreements.
Mr Trump believes his discussions will be different because Mr Kim has publicly announced his desire to focus on economic development in his reclusive nation, which is suffering under harsh US and international sanctions.
Mr Trump has favoured direct talks with Mr Kim, but with no third summit under discussion right now, the next stage of negotiations is likely to be conducted at lower levels.
On Wednesday, Mr Trump’s envoy to North Korea Steve Biegun had lunch at the State Department with his counterparts from Japan and South Korea. The South Koreans have proposed semi-official three-way talks with the United States and North Korea as it works to put nuclear diplomacy back on track.
Suh Hoon, the director of South Korea’s National Intelligence Service, told the parliament in Seoul that North Korea is restoring facilities at a rocket launch site it had dismantled last year in a goodwill measure.
Meanwhile, 38 North, a website specialising in North Korea studies, said commercial satellite imagery indicates the rebuilding started between February 16 and March 2.
And the Centre for Strategic and International Studies, a think tank in Washington, issued another report saying satellite imagery taken on Saturday – just two days after the summit ended – showed North Korea “pursuing a rapid rebuilding” of the rocket site.
Some analysts think the work is a signal that Mr Kim is getting ready to conduct more tests, but others suggest he is just registering his disappointment that no agreement was reached at the summit.
Joel Wit, a North Korea proliferation expert who helped negotiate with North Korea in the mid-1990s, said the new work at Sohae is Mr Kim’s way of showing that he is “getting impatient with lack of progress in negotiations”.