Hundreds of supporters of former Georgian leader Mikheil Saakashvili on Tuesday freed the detained politician from a police van amid a showdown with officers in central Kiev, AFP correspondents reported.
Earlier Tuesday Ukrainian security services arrested Saakashvili following his long-running feud with President Petro Poroshenko.
But hundreds of the 49-year-old politician's supporters surrounded the police van and he was later seen walking in the street.
With a handcuff on one hand and surrounded by the mass of people, Saakashvili urged them to march to the Ukrainian parliament and demand the impeachment of the president.
"There are millions of us, we are very strong," he said.
"We are going to parliament to demand the impeachment."
Saakashvili, who was a regional governor in Ukraine, fell out with Poroshenko over accusations that Kiev was failing to make good on the fight against corruption and was stripped of his Ukrainian passport.
In September, he defied the Ukrainian government and forced his way back into the conflict-riven country with the help of supporters.