Ukrainian security forces used tear gas against protesters demanding the release of the former president of Georgia, who was detained earlier on Tuesday.
Mr Saakashvili climbed on to the roof of his home in Kiev, drawing a crowd of supporters below, and threatened to jump off, Ukrainian media reported.
By the time officers had wrangled the former Georgian president and pushed him into the van waiting to transport him to jail, a large, restive crowd was waiting for them, too.
As president of Georgia, a former Soviet republic, he spent almost a decade in office campaigning against state corruption and perceived aggression by the Kremlin.
Before moving to Ukraine, Mr Saakashvili served for nearly ten years as president of Georgia.
The Security Service said in a statement that Mr Saakashvili is facing a criminal investigation for "assisting members of criminal organisations or hiding their criminal activities".
Given the drama that unfolded at his apartment building Tuesday, however, it's unlikely that Saakashvili plans to make this process easy on Ukrainian authorities.
Saakashvili's associate Siverion Dangadze was detained in an attempt to leave Ukraine, and documents that law-enforcement officials seized from him prove that he received funding from Serhiy Kurchenko, a fugitive associate of former Ukrainian President Viktor Yanukovych, Lutsenko said. He had already been stripped of his Ukrainian citizenship.
Saakashvili had been appointed by Poroshenko, an old friend, to help energize and transform Odessa in 2015, but by the end of the next year the relationship had ruptured and Saakashvili stepped down, vowing to oppose his former partner.
"What's going on in Kiev today is Ukraine's headache", Kremlin spokesman Dmitry Peskov said Tuesday, according to a Washington Post translation. "This is something you wouldn't wish even on an enemy, that's how I'd put it", he added.
Saakashvili has emerged as an anti-corruption campaigner in Ukraine.
The Guardian reports that Saakashvili responded by insisting "it was Poroshenko who was acting to benefit the Russian president".