A Ukrainian judge sentenced the feisty opposition leader to seven years in jail for abusing her powers in a 2009 gas deal with Russia, a verdict that is set to harm ties with the European Union.
Authorities braced for the announcement of the verdict by dispatching a large deployment of anti-riot police decked out in bulletproof vests to Kiev's main Kreshchatyk avenue where dozens of Tymoshenko's supporters and critics had pitched tents earlier in the day.
Riot police had to push back pro-Tymoshenko demonstrators as they tried to block a road, a police spokesman said, adding that around a dozen protesters were detained by Tuesday afternoon.
Police detained several protesters, including Tymoshenko supporters who sought to block the avenue, and topless activists from Ukraine's FEMEN group.
Some minor scuffles broke out but there were no major clashes, AFP correspondents reported from the scene.
"Freedom for Yulia!" and "Down with the bandits!" were among the slogans shouted by the demonstrators before the verdict was announced.
Activists from FEMEN, who have repeatedly slammed the trial as a "squabble between two criminal gangs" and are known for their motto "I came. I stripped. I conquered," staged another topless protest.
Donning traditional flower head garlands, the young women showed their anger by stripping to the waist and climbing onto the balcony of a department store in the city centre from where they brandished protest signs.
A Kiev police spokesman said the five FEMEN protesters were detained, along with seven Tymoshenko supporters who sought to block the main Kiev avenue.
"They are detained and are currently at a detention center," spokesman Volodymyr Polishchuk told AFP.