( CNN ) -- Opposition demonstrators smashed out windows and doors of a government building in Kiev and were using fireworks to smoke out police , according to a journalist at the scene Saturday in the Ukrainian capital . Opposition leaders said the demonstrators targeted the Ukrainian House because police were launching attacks against them from there , according to the journalist , Victoria Butenko . The increase in action comes after verbal clashes between Ukraine 's president and opposition leader Vitaly Klitschko on Saturday . On Saturday , President Viktor Yanukovych offered government posts to Klitschko and another leader of an opposing party , the presidential website said . Klitschko then announced the rejection of those offers on a public stage , where he was joined by heads of other political parties . Klitschko leads the Ukrainian Democratic Alliance for Reforms party ( UDAR ) and plans to run for president in 2015 . Arseniy Yatsenyuk , who heads the Fatherland Party , would have become the prime minister and , under the president 's offer , would have been able to dismiss the current government , which has been one of the protesters ' demands . The president also offered the post of deputy prime minister on humanitarian issues to Klitschko , a champion boxer known as `` Dr . Ironfist . '' The president also said he would agree to a working group to look at changes to the constitution , according to the president 's website . But Klitschko 's announcement rejected all parts of the offer , which came after a day of tension between police and hundreds of protesters who continued their vigil in Kiev 's Independence Square and surrounding streets . They have set up tent cities and put up barricades . Large plumes of black smoke billowed from the barricades as riot police watched and waited nearby . Protests against the government began in November when Yanukovych refused to sign a trade agreement with the European Union in favor of stronger economic ties with Russia . UDAR warned earlier Saturday that authorities are preparing to provoke peaceful protesters and may plant aggressors among the crowds in an effort to enact emergency rule . `` We call on all Ukrainian citizens not to succumb to provocations of authorities and continue the protest exclusively in a peaceful manner , '' a party statement said . A group of protesters blocked the entrance to the Energy Ministry on Saturday , a move Energy Minister Eduard Stavytsky called a direct threat to the entire energy system . Some protesters entered the building and argued with Stavytsky . `` Your action is illegal , '' Stavytsky told them . `` You have crossed the red line . You have entered a high security building . '' The protesters left the building saying they did not intend to undermine the work of the ministry in any way . The European Union is getting involved in the crisis . Next week , EU foreign policy chief Catherine Ashton and a European Parliament delegation are scheduled to visit Ukraine . Ukraine 's richest oligarch , Rinat Akhmetov , issued a statement Saturday saying business can not keep silent when people are killed . `` A real danger of breakup of the country emerges when a political crisis can lead to a deep economic recession , and thus inevitably result in lower standards of living , '' he said . Police say one officer was killed and another one stabbed in clashes with protesters . CNN 's Diana Magnay , Joseph Netto , Victoria Eastwood and journalist Victoria Butenko contributed to this story .
NEW : Protesters launch fireworks into government building in Russia morning early Sunday . NEW : Opposition says police were using the building to launch attacks on them . On a day the opposition leaders rejected Ukrainian president 's peace offer . President Victor Yanukovych had offered government posts to opposition leaders , according to a government statement .