A senior U.N. envoy who visited Pyongyang this month carrying a pressing appeal for diplomacy was told by his North Korean hosts that it was “too early” for steps that might ease the confrontation over their nuclear program.

“There was no sense of urgency” among North Korean officials, said one source familiar with the Dec. 5 to 9 journey by Jeffrey Feltman, the U.N. undersecretary for political affairs and a former senior U.S. diplomat. His trip, which has received relatively little attention, was the first to Pyongyang by a high-level U.N. official in six years.

The North Korean reluctance to enter talks now puts it on a potential collision course with the United States. President Trump warned this week: “America and its allies will take all necessary steps to achieve a denuclearization and ensure that this regime cannot threaten the world. . . . It will be taken care of.”

The exit ramps from this crisis appear to be narrowing in both Washington and Pyongyang, creating new worry, frustration and resolve. North Korea’s seeming disinterest in any early negotiations was “convincing diplomatic theater, if it was theater,” said one analyst.

Feltman made three requests of the North Koreans during his 15½ hours of talks, sources said. He proposed that they reopen military-to-military channels that were cut in 2009, so that the risk of accidental war might be reduced; he urged them to signal that they were ready to engage the United States in talks, following their Nov. 29 proclamation that North Korea had completed its “state nuclear force”; and he asked them to implement Security Council resolutions condemning their weapons programs.

To dramatize his message about the risk of unintended conflict, Feltman gave North Korean Foreign Minister Ri Yong Ho a copy of historian Christopher Clark’s study, “The Sleepwalkers: How Europe Went to War in 1914.” Ri was the most senior North Korean official Feltman met.

Feltman was carrying a letter from U.N. Secretary-General António Guterres to North Korean leader Kim Jong Un, arguing that Pyongyang’s attempt to gain nuclear deterrence could produce the very conflict that it seeks to avoid. Feltman’s message was reviewed before the trip by the United States, China, Japan, South Korea and Russia, the nations that joined in the “Six-Party Talks” with North Korea from 2003 to 2009 that sought unsuccessfully to halt its nuclear program.

Analysts interpreted the North Korean response as an indication that Pyongyang plans more missile and nuclear tests to convincingly demonstrate its ability to strike the U.S. mainland with a nuclear-tipped missile. “They don’t feel they are quite there yet,” said one source. Such additional North Korean weapons tests might trigger a U.S. response.

The North Koreans engaged in spirited exchanges with Feltman, posing many questions about U.S. decision-making, the sources said. But they were elusive when asked to explain how they wanted the United States to change its “hostile” policy toward the regime, and what they meant in the Nov. 29 announcement that North Korea had completed its state nuclear force.

The North Koreans evidently want to bargain, but from a position of maximum strength. They agreed, for example, that a restoration of military-to-military contacts would at some point be necessary, but not yet. They also agreed that denuclearization is the ultimate long-term goal for Korea, but not yet. And they expressed interest in a follow-up meeting, though nothing specific is planned.

One perversely encouraging sign is that after Feltman urged the North Koreans to engage the Security Council more closely, U.N. ambassador Ja Song Nam attended a Council discussion Friday with Guterres and senior diplomats focusing on the danger of accidental war on the Korean Peninsula.

In the 10 days since Feltman’s mission, concern about the danger of conflict has increased in Washington. Secretary of State Rex Tillerson reiterated last week that he wants talks with Pyongyang: “We’re ready to have the first meeting without precondition; . . . we can talk about the weather if you want.” But the White House was displeased, and Tillerson backtracked, saying that Pyongyang would have to “earn its way back to the table,” presumably by halting weapons tests. Tillerson’s aides say he just wanted “talks,” not negotiations.

A chilling warning came last week from national security adviser H.R. McMaster, who said that U.N. sanctions against North Korea “might be our last, best chance to avoid military conflict.” Asked Tuesday by CBS about the North Korean nuclear threat, McMaster said: “I don’t think we can tolerate that risk.”

The sleepwalkers of 2017 should consider: On the brink of conflict, you never know just where the edge of the cliff may be.