Associates of the former President of Georgia said he was detained by armed men in camouflage at a restaurant in Kiev and quickly driven to the capital city’s airport.
Last week, Mr Saakashvili’s lawyer said he could face imminent deportation or extradition after he lost a court appeal.
Oleh Slobodyan, a spokesman for the Ukrainian border guards, said on Facebook the agency’s personnel had to use force to counter his supporters at the airport.
“This person was on Ukrainian territory illegally and therefore, in compliance with all legal procedures, he was returned to the country from where he arrived,” Mr Slobodyan said.
Mr Saakashvili was admitted to Polish territory on a request from Ukrainian immigration authorities, Poland’s border guards said in a statement on the agency’s web site.
He was admitted to Poland as the spouse of a European Union citizen. Mr Saakashvili’s wife is Dutch.
Mr Saakashvili entered Ukraine last September, despite being stripped of his Ukrainian citizenship in a protracted standoff with authorities in Kiev, whom he accuses of corruption.
A video posted on Mr Saakashvili’s official Facebook page showed several men in green military uniform approaching a man lying on the floor of a restaurant.
“Unknown people in masks seized Mikheil Saakashvili and took him away… The kidnappers were in three white minivans,” a post on the same page read.
“There’s no legal reason for deportation. This is a kidnapping by Ukrainian bandits in order to get rid of a political opponent!” another post said.
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Mr Saakashvili was President of Georgia from 2004-13, left the country when his presidency ended and came to Ukraine as an ally of Petro Poroshenko, after the Euromaidan protests ousted pro-Russian President Viktor Yanukovych early in 2014.
Mr Poroshenko appointed him governor of the Odessa region, but he resigned from the post in 2016 and harshly criticised the President for failing to stem the official corruption that has crippled the country.
He was stripped of his citizenship last year when he was abroad, but forced his way back into Ukraine in September.
Since then, he has led repeated protests against Mr Poroshenko, who he alleges is corrupt.
There was no immediate sign of public outcry against the latest detention, unlike the street protests which allowed Mr Saakashvili to escape police custody in December – one of the more dramatic twists in his long-running cat-and-mouse game with the Ukrainian authorities.