WASHINGTON — Freed after more than a year in prison, three Americans flew homeward from North Korea late Tuesday toward a big middle-of-the-night celebration featuring President Donald Trump — the latest sign of improving relations between longtime adversaries in the buildup to a historic summit between Trump and North Korea’s King Jong Un.

Trump promised “quite a scene” at Joint Base Andrews outside Washington for the detainees, who were released as Secretary of State Mike Pompeo visited North Korea on Wednesday to finalize plans for the summit.

Singapore is the likely site, late this month or in early June, for the summit.

Trump made a point of publicly thanking North Korea’s leader for the prisoners’ release — “I appreciate Kim Jong Un doing this” — and hailed it as a sign of cooling tensions and growing opportunity on the Korean peninsula. Kim decided to grant amnesty to the three Americans at the “official suggestion” of the U.S. president, said North Korea’s official news agency, KCNA.

North Korea had accused Kim Dong Chul, Kim Hak Song and Tony Kim, all Korean-Americans, of anti-state activities. Their arrests were widely seen as politically motivated and had compounded the dire state of relations over the isolated nation’s nuclear weapons.

During his visit, Pompeo discussed the agenda for a potential Trump-Kim Jong Un summit. Pompeo said the summit is scheduled to last one day but could be extended by a day depending on how talks progress.

North Korea’s state-run media explicitly mentioned plans for the summit for the first time.