The back-channel talks were to be held in New York between the US experts and a six-member team of North Koreans led by Choe Son-hui, the director of the American affairs bureau of the country's foreign ministry.
Donald Zagoria, the head of the National Committee on American Foreign Policy, an advocacy group that was organizing the talks, emailed participants Friday morning to say next week's meeting would proceed as scheduled after receiving assurances that the visas would be granted, the two participants said.
But hours later, Zagoria sent a follow-up email to the group saying the visas were not approved and the talks were off.
The last-minute withdrawal of the approval of the visas came hours after the Malaysian government announced that VX nerve agent
was used to assassinate Kim Jong Nam, the estranged brother of North Korean leader Kim Jong Un, on February 13 at Kuala Lumpur International Airport as he waited to board a flight to Macau. The extremely toxic chemical is classified as a weapon of mass destruction by the United Nations.
South Korea has accused Pyongyang of ordering the killing, and the Malaysian government has implicated four North Koreans in Kim's death.
In canceling the talks, top Trump administration officials seem to have overruled State Department officials, who supported the talks, one of the people who planned to attend said.
"I think it was the VX that really made the difference," said the source, who spoke on the condition of anonymity because of the sensitivity of the matter. "Someone looked at this and said, 'Wait a minute, we should not be doing this right now.' "
Kim's death came on the heels of North Korea's ballistic missile test on February 12
, which coincided with Japanese Prime Shinzo Abe's visit with President Donald Trump. Abe was dining with the President
at his Mar-a-Lago resort in Palm Beach, Florida, when the launch took place.
Informal "track 2" talks allow policymakers and experts to exchange views outside the more constrained atmosphere of formal negotiations. North Korean and US experts have met in such settings in recent years in Berlin and Malaysia.
The last meeting in the US was in 2012, when a delegation from Pyongyang attended a closed-door conference in New York on security in Northeast Asia. John Kerry, then chairman of the Senate Foreign Relations Committee, met with the leader of the North Korean delegation, Ri Yong Ho, who at the time was the country's representative to the "six-party talks" with the US, South Korea, China and Russia over North Korea's nuclear weapons program. Ri is now North Korea's foreign minister.
The Obama administration did not approve visas for future talks, however, after the North Korea continued to provoke the US with nuclear and missile tests.
The group of Americans planning to take part in next week's talks included former US Ambassador to China Winston Lord, Robert Gallucci, who served as a negotiator with North Korea under President Bill Clinton, and Victor Cha, a top Asia adviser to President George W. Bush. Evans J. R. Revere, a former principal deputy assistant secretary of state specializing in North Korea, was also scheduled to attend.
Although no currently serving American officials were scheduled to take part in the meeting, it would have signaled a potential for future progress if the Trump administration would have approved the visas. The American participants would also have briefed the administration on the discussions.
"It would have signaled a new start and suggest the Trump administration was more open to discussion," one of the participants said. "In that sense there could have been a little movement.
Additionally, had the informal talks gone forward, North Korea might have tempered its usually bellicose reaction to the annual joint military drills between the US and South Korea, set to begin next month, the sources said.
But they stressed that such a development "wouldn't have necessarily been a springboard" for the resumption of the six-nation disarmament talks.
A State Department spokesperson would only say, "The U.S. government had no plans to engage in track 2 talks in New York. We do not discuss details of individual visa cases."