UNITED NATIONS — Former U.N. secretary-general Ban Ki-moon said Wednesday the dialogue between the two Koreas that began during the Winter Olympics must be kept alive so it can hopefully lead to reconciliation, peace and the denuclearization of North Korea.

Ban, who was South Korea’s foreign minister before serving 10 years as U.N. chief, told the U.N. Security Council on Wednesday that the “current reconciliatory atmosphere must be nurtured by continuing engagement of both South and North Korean authorities.”

He said the United States can also play “a crucially important role” by engaging with North Korea, as South Korean President Moon Jae-in has suggested.

On Tuesday, the Trump administration disclosed that Vice President Mike Pence was set to hold a history-making meeting with North Korean officials during the Olympics, but Kim Jong Un’s government canceled at the last minute.

A potential high-level interaction between the U.S. and North Korea, which would have broken years of estrangement between the two countries, loomed prominently over the Winter Games, where North Korea in a last-minute move sent 22 athletes to compete on a combined team with South Korea, the host of the games.

Kim also sent more than 400 others to the Olympics including his younger sister, a 140-member orchestra, an all-female 229-member cheering squad and a demonstration taekwondo team. All the North Koreans became major attractions in the South because of the rarity of contacts with the isolated North, and the possibility of reduced tensions after a year of escalating rhetoric and Kim’s increasingly sophisticated nuclear and ballistic missile tests.

Ban echoed the assessment of his successor, Secretary-General Antonio Guterres, that the situation on the Korean Peninsula is the “most serious and imminent challenge at this time.”

But he said North Korea’s participation in the Olympic games in Pyeongchang has raised hopes and expectations around the world.

“I sincerely hope that this good reconciliatory move will continue through a genuine and meaningful dialogue which will address all the issues — first of all the conciliatory process between the South and North leading to U.S.-North Korean talks for more meaningful and constructive denuclearization dialogue,” Ban told reporters. “And that will be the process which I envision.”

He urged North Korea in the speech to a Security Council meeting on the U.N. Charter’s role in maintaining peace to abide by U.N. resolutions, which have imposed increasingly tough sanctions to deter Pyongyang’s nuclear program. And he urged all U.N. member states “to do their part to help resolve the North Korean nuclear issue through diplomatic efforts.”

“We must keep alive this hard-won momentum for dialogue so that the narrow window of opportunity provided by this newly created momentum will be able to lead to a more meaningful and genuine dialogue process of reconciliation, peace and ultimate denuclearization of North Korea,” Ban said.

He said denuclearization would also help spur peace and stability in northeast Asia.

“This process also requires wholehearted support of the United Nations, and I count on the Security Council in moving the whole process towards this end,” Ban said.

U.S. Ambassador Nikki Haley told the council meeting there’s still a long way to go.

“The Security Council has done admirable work to address the threat of North Korea. But too many member states have failed to abide by their Charter obligation to enforce the sanctions this council has imposed,” she said.

“In the meantime, Pyongyang continues to develop its nuclear arsenal, threaten its neighbors, and categorically refuse to discuss denuclearization,” Haley said. “We must do better.”