The historic summit planned between President Trump and North Korean leader Kim Jong Un is expected to take place in Singapore in early June, Fox News has learned.

That summit would be the first-ever meeting between a U.S. president and a North Korean leader.

On Wednesday, Secretary of State Mike Pompeo arrived in North Korea to finalize details of the meeting and secure the release of three detained American citizens. President Trump is expected to meet those citizens when Pompeo’s plane lands early Thursday morning.

Pompeo flew out of Washington under cover of darkness late Monday aboard an Air Force 757 accompanied by a handful of senior aides, a security detail and two journalists: one from The Associated Press and one from The Washington Post, who were given roughly four hours' notice of his departure. The flight arrived Wednesday morning, and North Korean officials were on hand to greet the American diplomat.

AMERICAN PRISONERS HELD IN NORTH KOREA ON THEIR WAY HOME AFTER POMPEO VISIT, TRUMP SAYS

A Trump-Kim meeting seemed a remote possibility just a few months ago, when the two leaders were trading threats and insults over North Korea's development of nuclear weapons and a string of ballistic missile tests. But momentum for diplomacy has built this year; North and South Korea have moved to ease tensions, including with their own leaders holding a summit late last month.

In March, Trump unexpectedly accepted an offer of talks from Kim after the North Korean dictator agreed to suspend nuclear and missile tests and discuss "denuclearization." According to South Korea, Kim says he's willing to give up his nukes if the United States commits to a formal end to the Korean War and pledges not to attack the North.

On Monday, China's official news agency, Xinhua, quoted Kim as saying, "I hope to build mutual trust with the U.S. through dialogue." He added that a political resolution of tensions on the Korean Peninsula and denuclearization should proceed in stages, with all sides moving in concert.

But his exact demands for relinquishing the weapons his nation has spent decades building remain unclear. Previous U.S. efforts to negotiate an end to the North's nuclear weapons program failed under Presidents Bill Clinton and George W. Bush.

Fox News’ Madeline Farber and The Associated Press contributed to this report.