Right-wing protesters scuffled with police in Kyiv as dozens rallied outside the Russian Embassy, where a polling station was set up for Russian citizens to vote in their country's parliamentary elections.
Nationalist Svoboda party leader Ihor Miroshnichenko, who was among the demonstrators on September 18, said Ukraine should not allow “the enemy and state aggressor” to conduct illegal elections in Ukraine.
One demonstrator was detained in a scuffle with police after a few nationalists tried to stop Russian citizens from voting. It was unclear how many Russians actually did cast ballots by day's end.
Scuffles also broke out near the building of the Russian Consulate in Ukraine's Black Sea port city of Odesa.
WATCH: Scuffles At The Russian Consulate In Odesa (natural sound)
Russia is holding national elections for the lower house of parliament. The vote is also taking place on the Ukrainian peninsula of Crimea, the first time since Moscow's annexation of the territory two years ago.
That has angered the Ukrainian government, with Foreign Ministry spokeswoman Maryana Betsa saying voting in the Russian election could not take place in her country.
About 80,000 Russian voters live in Ukraine, Russian electoral officials say.
Based on reporting by AP, TASS, Interfax, and the BBC