Protesters have thrown eggs and stones at the Russian embassy in Kiev to demand the release of hunger-striking Ukrainian pilot Nadia Savchenko.
She is on trial in Russia after being captured while fighting pro-Russian rebels in eastern Ukraine in 2014.
Ms Savchenko is accused of directing artillery fire that killed two Russian journalists - a claim she denies.
Later on Sunday, Ukraine's embassy in Moscow was also pelted by eggs as dozens of people rallied outside.
Relations between Ukraine and Russia have deteriorated following Moscow's annexation of the Crimea peninsula in 2014 and its support for pro-Russian rebels in eastern Ukraine.
On Sunday, several thousand people began the protest in Kiev's central Maidan Square, before hundreds of protesters moved on to the embassy several kilometres away.
Demonstrators were later seen throwing eggs and stones at the embassy and removing a security camera.
The Russian embassy has formally complained to Ukraine about separate attacks on its property overnight on Saturday.
Three cars were "seriously damaged" by unknown assailants, who also set off smoke bombs, embassy spokesman Oleg Grishin said.
Police described the case as hooliganism.
Ms Savchenko, 34, has become a heroine in Ukraine and is seen as a symbol of the country's resistance against Russia.
She began a hunger strike without water on Friday to protest against the sudden adjournment of her trial the previous day, as she was about to deliver a closing statement.