Stone-throwing protesters have clashed with police in central Kiev amid tensions over proposed changes to the constitution. Thousands of protesters attacked the ruling-party headquarters and tried to march on parliament, reports said. Tumultuous scenes have also been reported inside parliament where opposition MPs are pushing for a vote on replacing the constitution. The move is aimed at curbing President Viktor Yanukovychs powers. The opposition has repeatedly warned that failure to act will further inflame mass anti-government protests. Ukraines unrest began in November, when Mr Yanukovych backed away from an association and free trade deal with the European Union, and instead agreed to a loan from Russia. Moscow wants Ukraine to join the Russia-led customs union, where Belarus and Kazakhstan are also members. Both the EU and Russia have accused each other of interfering in Ukraines affairs. Doors locked Tens of thousands of protesters trying to march on the parliament building have been blocked by lines of police vehicles, according to reports from Kiev. Some are ripping up cobblestones to throw at police, and others are throwing smoke bombs, while police are responding with stun and smoke grenades and rubber bullets. Protesters also attacked the headquarters of President Yanukovychs ruling party. Several people have been injured, both protesters and police officers, local media reported. Inside parliament, reported Interfax-Ukraine news agency, about 50 opposition MPs blocked the parliamentary rostrum in protest after parliamentary staff refused to register their resolution on reinstating the 2004 constitution. Our deputies have just returned from the draft law registration section. They have just simply locked the doors there on the instructions of [Speaker Volodymyr] Rybak and are refusing even to talk to Ukrainian peoples deputies, let alone register the resolution, opposition leader Arseniy Yatsenyuk was quoted as saying. The opposition has been pushing for weeks for a return to the 2004 constitution, which would mean President Yanukovych losing some of the powers he has gained since his election in 2010. The changes would mean that parliament - not the president - would appoint the prime minister and most cabinet members, as well as regional governors. The move could also lead to snap presidential elections - a key demand of the opposition. MPs who support the president have argued that different proposals on how to return to the previous constitution legitimately have not been thoroughly discussed, and more time is needed to iron out all the differences between the two sides. In a separate development, Russian Finance Minister Anton Siluanov said Moscow would provide Ukraine with a new 2bn (1.2bn) tranche of aid this week. In December, Moscow pledged 15bn to back Ukraines struggling economy, but so far only 3bn has been transferred. The Kremlin had hinted it would freeze the aid until a new government acceptable to Moscow was formed after Ukrainian PM Mykola Azarov resigned last month. On Monday, an amnesty for anti-government protesters in Ukraine came into force after demonstrators ended their occupation of government buildings in Kiev and in the regions. Protesters had held some of the buildings for more than two months. But a sprawling tent city remains in Kievs central square, where some denounced the decision to end the occupations. TAGS: abc breaking news, bbc, bbc football, bbc iplayer, bbc news, bbc news america, bbc persian, bbc sport, bbc weather, bbc world news, breaking celebrity news, breaking election news, breaking late news, breaking local news, breaking music news, breaking news, breaking news alerts, breaking news canada, breaking news headlines, breaking news in atlanta, breaking news in nigeria, breaking news india, breaking news pensacola florida, breaking news plane crash, breaking news story, breaking sports news, business expensive news home media world, christian world news, cnn, cnn breaking news, cnn money, cnn news, cnn news breaking news, cnn news world, detroit breaking news, global news, headline, headline news, health care technology news, hot latest global news, internet technology news, las vegas breaking news, latest breaking news, latest celebrity news, latest information technology news, latest music news, latest news, latest news headlines, latest news update, latest sports news, live breaking news, local breaking news, local news today, msn breaking news, nbc breaking news, nbc world news, news of the world, news report us world, news today news, news updated daily, solar technology news, sports news today, technology news, the latest news, today news, us news and world, us news and world report, us news and world report magazine, us news and world report web site, us news world report, world news, world news daily, world news headlines