The deal struck on Wednesday was the latest to emerge from a series of negotiations stretching back more than a year between Coale and Belarusian President Alexander Lukashenko, a close ally of Russian President Vladimir Putin.
Coale has been tasked by President Donald Trump with securing the release of hundreds of people including human rights campaigners, political activists, journalists and lawyers.
The US diplomacy is sensitive because Lukashenko, in charge of the former Soviet state since 1994, has long been shunned by the West for repressing his opponents and supporting Russia's war in Ukraine.
"This (process) has been very successful. President Trump's very happy with this," Coale told Reuters in the Lithuanian capital Vilnius, where the freed prisoners were taken.
The figure of 25 releases was much lower than the 250 that Coale negotiated when he last visited Minsk in March.
But the American said in an interview that he expected to return in about a month and hoped at that point that "hundreds" would be freed.
Human rights group Viasna, which is banned in Belarus as an extremist organisation, said many of those released on Wednesday had been sentenced to many years in prison. One of them, journalist Andrei Alyaksandrau, had been serving a 14-year term.
Also released were a trio of musicians, arrested in 2022, whose songs were designated as "extremist materials".
A source familiar with the situation told Reuters that, in addition to the 25, a significant number of prisoners were expected to be freed and remain inside Belarus.
Viasna said relatives of some detainees had been told they could collect their loved ones from penal colonies on Wednesday morning.
Viasna says Belarus still holds 886 political prisoners, although Lukashenko rejects that label and denies charges by the exiled opposition that he is steadily arresting more people to replace those he releases.
Asked if he was sticking to an earlier prediction that all the prisoners could be freed this year, Coale told Reuters: "Well, I think so. (I'll) give it a try."
The 79-year-old has previously admitted to resorting occasionally to crude humour in order to win over Lukashenko, and discreetly emptying his glass on the floor in order to avoid getting drunk at long vodka sessions.
Coale said earlier that the US was lifting sanctions on Lakokraska, a manufacturer of paints and industrial coatings, and Bellesbumprom, a state-owned industrial concern that oversees the forestry, pulp and paper sectors.
He also promised Lukashenko on Tuesday to get US banks to hand back tens of millions of dollars in frozen Belarusian assets.
Coale's humanitarian efforts have earned gratitude from many Belarusians, but rights groups and opposition politicians say arrests continue and Lukashenko has yet to end repression.
"Today, alongside our joy for those released, we remember those who remain behind bars," exiled opposition leader Sviatlana Tsikhanouskaya posted on X.
Asked what obstacles remained in the way of his diplomacy, Coale cited the wars in the Gulf and Ukraine.
"Look, if these wars weren't going on, we would get everybody out by next Tuesday. But the wars complicate our government, they complicate Belarus' government and everybody else in the world right now," he said.
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