( CNN ) -- The chief of police in Kiev , Ukraine , Valeriy Koryak , has resigned after riot police used `` excessive force '' against anti-government protesters , police said . Riot police stepped in early Saturday and dispersed several hundred people who came to Independence Square in support of Ukraine 's European integration . Seven people were hospitalized and dozens arrested . The United States condemned what it called `` violence against protesters '' in a statement posted online by the U.S. Embassy in Kiev . Ukrainian Interior Minister Vitaliy Zakharchenko later apologized , saying riot police abused their power . He promised a thorough investigation . But he also warned protesters via state television against improper behavior , saying `` if there are calls for mass disturbances , then we will react to this harshly . '' A massive crowd of protesters , estimated to number at least 100,000 , gathered Sunday in Independence Square . Some were seen setting objects on fire and throwing them at security forces . Others broke through a police barrier that was guarding a Christmas tree , climbed the tree and topped it with the Ukrainian flag . CNN 's Zarifmo Aslamshoyeva contributed to this report .
Kiev 's police chief resigned after riot police violence against protesters , protesters say . Anti - government demonstrators continue to clash with security on Sunday . Interior Ministry calls for violence , but urges police to cooperate .