Kiev , Ukraine ( CNN ) -- Demonstrators packed Kiev 's Independence Square in freezing temperatures on Sunday , rallying in defiance of new laws that set limitations on the right to protest . Protesters and police accused each other of attacks during the large demonstration , which stretched into the early morning hours . Ukraine 's Interior Ministry said protesters , wearing masks and helmets , used flares , tear gas , baseball bats and stones in clashes with police , breaking doors and windows on police buses and trying to take over government buildings . Video from the scene showed protesters and police squaring off , with demonstrators hurling Molotov cocktails toward officers . The ministry said 30 police were injured , and one was taken hostage by the protesters and later released . A post on a Facebook page for Olesia Orobets , an opposition lawmaker , said she had been attacked by police and her phone had been taken away . Estimates of the number of protesters in the capital 's square varied widely . At least four of them were detained by police , the Interior Ministry said . Negotiations possible . Sunday 's protest marked the latest fallout over legislation that was approved Thursday by lawmakers loyal to Ukraine 's pro-Russian President Viktor Yanukovych , who signed it into law soon afterward . Amid the clashes , there were some signs that the opposing sides might soon sit together at the negotiating table . Opposition leader Arseniy Yatsenyuk said Sunday that he had received a call from Yanukovych saying the government was prepared to negotiate with the opposition . The President 's office said he was creating a working group to overcome the political crisis and had ordered it to meet with the opposition . The clashes and possible move toward talks come in the wake of weeks of public protests after Yanukovych 's decision in November to spurn a planned a trade deal with the European Union and turn toward Russia instead . The new law includes provisions barring people from wearing helmets and masks to rallies and from setting up tents or sound equipment without prior police permission . Opposition politicians have objected to the way that Yanukovych 's Party of Regions pushed the bill through the parliament , the Verkhovna Rada . Vitali Klitschko , an opposition leader and former heavyweight boxing champion , said the law -- which was adopted by a show of hands -- was `` invalid , '' according to his UDAR party 's website . He stood between the police and the crowd in the square , trying to prevent violence . The far-right Svoboda Party said in a news release that people were `` outraged by the Party of Regions actions at the Verkhovna Rada and their recently adopted draconian laws . Protesters are demanding resignation of the government and asking the authorities to stop the persecution of activists . '' Kerry : 'Anti-democratic ' steps . The U.S. Embassy called for an end to the violence in the streets Sunday . `` We further urge the Government of Ukraine to immediately start negotiations with all sides to resolve the political standoff , address protestors ' concerns , and prevent violence from spreading , '' the embassy said Sunday . `` Violence only serves to foster fear and confusion , and distracts from the need for a political solution , which is the best way to carry out the will of the Ukrainian people . '' U.S. Secretary of State John Kerry also criticized the new legislation in remarks Friday , saying it was `` rammed through '' the parliament `` without transparency and accountability '' and that it `` violates all the norms '' of the European Union . `` We believe deeply that the people of Ukraine want to affiliate and want to be associated with Europe and they want to turn in that direction , '' Kerry said . `` And the steps that were taken yesterday are anti-democratic , they 're wrong , they are taking from the people of Ukraine their choice and their opportunity for the future . '' In December , despite weeks of protest by anti-government protesters , Yanukovych agreed to a deal with Russia 's President Vladimir Putin for Moscow to buy Ukrainian debt and slash the price Kiev pays for its gas . The tumult in Ukraine goes to the heart of its future ties with Russia and the rest of Europe . Ukraine is split between pro-European regions in the west and a more Russia-oriented east . The protests have unfolded since November 21 , when Yanukovych changed his stance on the EU trade pact , which had been years in the making . The demonstrators say an EU agreement would open borders to trade and set the stage for modernization and inclusion . Ukraine 's government said the terms needed to be renegotiated to better protect Ukrainians . Journalist Victoria Butenko reported from Kiev and Laura Smith-Spark wrote in London . CNN 's Joseph Netto contributed to this report .
NEW : The President 's office says a working group will meet with the opposition . Comment: Interior Ministry says some protesters tried to march on government buildings . The new law was passed by lawmakers loyal to Ukraine 's president in a show of hands .