A few thousand protesters in Kyiv called for the removal of President Petro Poroshenko, while Ukrainian nationalists separately smashed windows and defaced three Russia-linked buildings in a day of demonstrations in the capital.
The anti-Poroshenko rally on February 18 was called by opposition figure Mikheil Saakashvili -- who was expelled from Ukraine on February 12 -- as part of what he has labeled an anticorruption campaign.
Officials estimated some 2,500 people gathered to demand Poroshenko’s resignation, while some 3,000 police were deployed to keep order. The French AFP news agency estimated that the crowd numbered as many as 10,000 people.
Smaller demonstrations were reported in other cities in western and central Ukraine.
Poroshenko and Saakashvili are former allies who are now bitter rivals.
Poroshenko invited Saakashvili to serve as governor of the Odesa region in 2015, but Saakashvili resigned after 1 1/2 years, complaining of massive corruption under Poroshenko.
Saakashvili was stripped of his citizenship in July 2017 and, after leading an opposition campaign against Poroshenko, was detained at a Kyiv restaurant on February 12 and taken to the airport and flown to Poland.
He eventually flew to the Netherlands, his wife's home country, and vowed to continue his battle to topple Poroshenko.
Meanwhile, Russian officials urged Kyiv to condemn "yet another provocation" after several dozen Ukrainian far-right nationalists damaged a Moscow-based aid agency and two Russian-owned banks in the capital.
Russian media on February 18 reported that Ukrainian demonstrators broke windows and used paint to deface the building housing the Rossotrudnichestvo aid agency.
Eleonora Mitrofanova, the head of the Rossotrudnichestvo agency, told journalists in Moscow that no one was injured in the attacks on the Kyiv headquarters, but "quite significant damage was done to the building."
Windows were also smashed at two Russian-owned banks, Sberbank and Alfa Bank.
A day earlier, nationalists gathered at the Rossotrudnichestvo building, ripping the Russian flag off the building and burning it.
The Russian Embassy in Kyiv said that "we hope the Ukrainian side will publicly condemn this incident -- the anti-Russian march and the attack on the Russian center."
Ukraine, once part of the Soviet Union, and Russia are bitter rivals. Moscow has annexed Western-leaning Ukraine's Crimea Peninsula and has backed separatists in eastern Ukraine fighting the government in Kyiv.