The feminist group's protesters, whose chests were painted blue and yellow -- the color of Ukraine's flag -- hoisted a placard against Putin and another calling for US-EU action.
Inna Shevchenko, a Femen leader, told reporters the protest was "in support of the Ukrainian people, in support of the Ukrainian revolution against Putin, against Russian occupation."
The activists called on the United States and European Union to impose sanctions "much more serious than just restrictions of visas" and freezing of assets of officials.
The United States on Thursday slapped visa bans on Russians and Ukrainians it blames for destabilizing Ukraine, setting the stage for more sanctions to come.
In an executive order, US President Barack Obama also authorized freezing the assets of officials and individuals involved in such action.
"Putin is scared of one thing -- he's scared of the people's power. He's not scared of the US or EU; he's playing games," Shevchenko added at the end of the short protest, which took place in glacial cold.
Femen is a long-standing Ukrainian group whose members have drawn attention worldwide with nude stunts targeting a range of political and religious figures.
The group takes aim at sexism and discrimination against women in addition to homophobia, church-and-state collusion, totalitarian regimes and electoral fraud.
Two Femen protesters were arrested in Crimea's capital Simferopol on Thursday after staging a topless demonstration against Russia's intervention in Ukraine in front of the regional parliament.