Saakashvili had been residing in Ukraine "illegally" and was therefore sent to the country where he initially came from, the service said in a statement.
Saakashvili during a press conference in Warsaw on 13 February. All this shows is how weak they are.
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"He was kidnapped by men in camouflage gear in a restaurant near our party offices".More news: GoFundMe created for 19-year-old Lizette Cuesta fatally stabbed by friends
The politician said that he was staying in a hotel in Poland, and that the Polish authorities had provided him with bodyguards. "They didn't show any identification".
Saakashvili, who is in conflict with his former ally President Petro Poroshenko, was abducted from a restaurant in the Ukrainian capital of Kiev yesterday. Saakashvili resigned from his post in November 2016 and became a vocal anti-government activist, which later led Poroshenko to strip Saakashvili of his Ukrainian citizenship while he was overseas. Poroshenko responded by stripping Saakashvili of his Ukrainian citizenship while the Georgian-born politician was in the United States.
Mikheil Saakashvili, who after leaving Georgia gained Ukrainian nationality and was governor of the Ukrainian region of Odessa, was arrested on several occasions last December on suspicion of "participating in criminal organisations" and planning an eventual coup. Saakashvili called the charges absurd and politically motivated. He has also been charged by Kiev with involvement in a Russian-led plot to destabilize Ukraine, an accusation he describes as "lies".
Opinion polls indicate that Saakashvili and the political movement he has created have only limited popularity in Ukraine, where parliamentary and presidential elections are due to be held in 2019. "Poroshenko will answer for this!" shouted supporters, according to an online stream of the protest.