Opinion polls indicate that Mr. Saakashvili has not won a large public following in Ukraine, where he studied as a student during the Soviet Union. But he has nonetheless been a major thorn in Mr. Poroshenko’s side by putting a spotlight on allegations of official corruption, an issue that mobilized street protests against Mr. Poroshenko’s predecessor Viktor F. Yanukovych in the winter of 2013-14.
Mr. Saakashvili went to Ukraine after the protests toppled Mr. Yanukovych and became a keen supporter of Ukraine’s new president, Mr. Poroshenko, who appointed him governor of Odessa, a Ukrainian region on the Black Sea notorious for corruption. Stripped of his Georgian citizenship by the authorities there, Mr. Saakashvili became a Ukrainian citizen in 2015.
But after a bitter falling out with Mr. Poroshenko, he was stripped of that nationality, too, and quit as Odessa’s governor, accusing the authorities in Kiev of enabling the corrupt deals they had vowed to uproot.
By sending him to Poland, Ukraine seems eager to remove the former Georgian leader, who has spearheaded a noisy opposition campaign against graft, as a potential political danger without jeopardizing his freedom.
Georgia, which Mr. Saakashvili governed until 2013, has requested that Ukraine hand him over to its own judicial system to face a litany of charges relating to his time in office. A court in Georgia last month sentenced Mr. Saakashvili in absentia to three years in prison for abusing his pardon powers as president.
Mr. Saakashvili has denounced the charges against him in Georgia as politically motivated, and said the same about efforts by the Georgian authorities in recent months to have him detained.
Ukraine’s previous efforts to detain Mr. Saakashvili were repeatedly thwarted by court orders and the intervention of Mr. Saakashvili’s supporters, who in December freed him from detention. A court last month rejected a request by prosecutors that Mr. Saakashvili be placed under house arrest and ruled that he could only be confined to his residence at night.
In an interview with Ukrainian media by telephone from Poland, Mr. Saakashvili denounced various charges against him as a “total falsehood” and accused Mr. Poroshenko of acting in concert with the President Vladimir V. Putin of Russia and the former Georgian leader Bidzina Ivanishvili “to get rid of me.”
Mr. Poroshenko “is not a president and not a man, but a sly profiteer who wants to ruin Ukraine,” Mr. Saakashvili said. “It all shows how weak they are. We will definitely win.”