United States President Donald Trump is waiting to receive a letter from his North Korean counterpart Kim Jong Un, a much-anticipated moment as preparations for a historic nuclear summit gain pace.

Kim’s right-hand man, Kim Yong Chol, was due in the US capital a day after talks in New York with Secretary of State Mike Pompeo made what the US diplomat called “real progress” towards holding the planned June 12 summit.

Meanwhile, back in Pyongyang, the North Korean leader re-committed his isolated state to “denuclearization,” boosting hopes of what would be an extraordinary diplomatic turn-around just a week after Trump threatened to cancel preparations.

Since that short-lived crisis, diplomats in both countries have conducted an intense flurry of negotiations, culminating on Thursday when Pompeo sat down in New York with Kim’s envoy.

Simultaneously, Kim met Russia’s Foreign Minister Sergei Lavrov and, according to official news agency KCNA the North’s “will for denuclearization of the Korean peninsula still remains unchanged, consistent and fixed.”

It is still unclear that North Korea’s vision of “denuclearization” in exchange for security guarantees and sanctions relief will prove compatible with Washington’s demand for a “complete, verifiable and irreversible” end to its nuclear program.

Many observers expect Kim, perhaps with tacit Chinese backing, to demand that Washington also reduces its own military footprint in South Korea and loosen its guarantees to treaty ally Japan.

But Pompeo suggested things are moving in the right direction.

“It will take bold leadership from Chairman Kim Jong Un if we were able to seize this once in a lifetime opportunity to change the course for the world,” he said.

“President Trump and I believe Chairman Kim is the kind of leader who can make those kind of decisions, and in the coming weeks and months, we will have the opportunity to test whether or not this is the case.”