Protesters against the adoption of Ukraine's new anti-dissent law turned violent Sunday, as protesters and police began to clash near the city's central square.
The demonstration, which continues a string of rallies that began when President Viktor Yanukovych pulled back from an association agreement with the European Union in November, erupted when protesters began attacking police with sticks, Reuters reported. Photos on social networks also showed groups of protesters attacking and burning a bus.
The Ukrainian news service UNIAN reported that riot police fought several hundred masked men using batons and tear gas.
The rally began peacefully, as tens of thousands of demonstrators filled the city's Maidan Square despite Friday's passage of a bill that essentially criminalizes the anti-government protests that have called for closer integration with Europe.
The measure provides up to a 15-year prison term for "mass violation" of public order. The bill also bans unauthorized tents, setting up stages or wearing helmets and masks at rallies, a measure many protesters openly violated Sunday.
While noting that more protesters were arriving, UNIAN estimated the crowd at 100,000 people on Sunday afternoon.
Western countries widely condemned a police crackdown on the rallies during their early stages last year and have criticized the new law as a restriction on Ukrainians' freedom of speech. U.S. Secretary of State John Kerry called the measure "anti-democratic" and "wrong."
Ukrainian Foreign Minister Leonid Kozhara said Friday that comments made against the law by diplomats like Kerry amount to foreign interference in the country's affairs and that the restrictions are in line with democratic norms.
The recently-passed law also places restrictions on nongovernment organizations, requiring them to register as "foreign agents" if they receive money from abroad. Russia passed a similar measure in late 2012 that has been widely criticized by human rights organizations.
After abandoning a planned Association Agreement with the EU, Yanukovych struck a deal with President Vladimir Putin and received a $15 billion bailout for Ukraine's debts in addition to highly-subsidized natural gas.
Speaking at the rally Sunday, opposition politician and boxing champion Vitaly Klitschko said that the opposition was announcing a new presidential election and that another protest would be held on Monday.