Rallies initially began Friday in Kiev after the Ukrainian government backed down from the culmination of four years of free trade negotiations with the European Union, The New York Times said.
In what is likely the largest public demonstration in Ukraine since the 2004 Orange Revolution, thousands of protesters gathered Sunday at European Square and on Bankova Street where the Presidential Administration is located, the Kiev Post reported.
Kiev police said there were about 22,000 protesters, but Oleksandr Turchynov, an opposition MP from the Fatherland parliamentary faction said some 100,000 were gathered.
Police said they used tear gas, but only against protesters who also used tear gas or threw smoke bombs at police, RIA Novosti reported.
Some demonstrators allegedly threw stones at police officers who were blocking the path to the Cabinet of Ministers, injuring one, the Post said.
Prime Minister Mykola Azarov said the cause of the abandoned EU agreements was the harsh terms set by the International Monetary Fund, but critics said the real reason was because Russia threatened to cut off gas supplies to the indebted country.
"I came here to support European values," said Oleksiy Zahumny, a 29-year-old wrapped in a European Union flag. "I'm sure this protest will reach its aim. Maybe not soon, but for sure we will win."