Police – outnumbered by protesters armed with firebombs – respond with stun grenades, teargas and water cannon Share your videos and photos of the protests , but remember your safety is most important

The sound of stun grenades continue to ring out and charred vehicles are smouldering in Kiev after a night of fierce clashes between protesters and police.

Ukranian police used cold water to disperse protesters as temperatures plunged in Kiev. Photograph: Julia Kochetova/Demotix/Corbis

The leaders of the opposition, including former heavyweight boxer Vitali Klitschko, dismissed the violence as the work of "provocateurs" and were due to hold negotiations with the government later on Monday.

The anti-government protests, which have beset Kiev for two months, escalated into fiery street battles with police on Sunday as thousands of demonstrators threw rocks and firebombs and set police vehicles on fire. Dozens of protesters were injured and 100 police sought medical attention, with 61 being admitted to hospital.

Police responded with stun grenades, teargas and, for the first time in the country's history, water cannon, but were outnumbered by the protesters. Many of the riot police held their shields over their heads to protect themselves from the projectiles thrown by demonstrators on the other side of a cordon of buses.

A protester throws stones over burning police cars. Photograph: Sergey Dolzhenko/EPA

The violence was a sharp escalation of Ukraine's two-month political crisis, which has brought round-the-clock protest gatherings, but had been largely peaceful. President Viktor Yanukovych last week signed an array of laws severely limiting protests and banning the wearing of helmets and gas masks. Many of the demonstrators wore hardhats and masks in defiance of the new laws.

Klitschko, the leader of the Udar (Punch) opposition party, tried to calm the demonstrators down, but failed and was sprayed by a fire extinguisher in the process. "What you are doing now presets a huge danger," the reigning world heavyweight boxing champion shouted to them.

Opposition leader Vitali Klitschko, right, is attacked and sprayed with a fire extinguisher as he tries to stop clashes between police and protesters in Kiev. Photograph: Efrem Lukatsky/AP

Klitschko, who said he would participate in presidential elections scheduled for spring 2015, then urged Yanukovych to announce snap presidential elections to relieve tensions. "I'm calling on Yanukovych to find strength and not repeat the fate of Ceaucescu and Gaddafi," he said, referring to the former Romanian and Libyan dictators.

He later travelled to Yanukovych's residence at Mezhyhirya outside Kiev and said the president has agreed to negotiate. Yanukovych said on his website that he had asked a working group, headed by national security council head Andriy Klyuev, to meet opposition representatives to work out a solution to the crisis.

Opposition supporters armed with clubs tried to break through a police blockade and storm the Ukrainian parliament Photograph: Sergey Dolzhenko/EPA

Late last night hundreds of radical activists stormed the police cordon, attacking riot police with sticks and chains in an attempt to push their way towards the Ukrainian parliament, in front of which were parked rows of police buses.

Wearing masks and helmets to disguise their identities and equipped with sticks, chains and shields, the protesters threw stones that they had prised out from the pavement. They burned four police buses and two lorries that were blocking the road, which led to 70 policemen being wounded and 40 hospitalised, the police press service reported. With temperatures hovering at -7C, the police responded with the stun grenades and water cannon. People shouted: "Epiphany!" in response, a reference to the Orthodox Christian holiday, celebrated on Sunday, when many Ukrainians traditionally plunge into ice holes.

A police bus is set on fire by protesters. Photograph: Gleb Garanich/Reuters

The police also fired rubber bullets at the protesters, medical volunteers working at the scene told the Guardian. The official opposition claimed they had nothing to do with the "provocateurs" who fought with police.

A number of western politicians and officials condemned the violence in Kiev. The US embassy said: "We urge calm and call on all sides to cease any acts provoking or resulting in violence."

Ukrainian riot police hit by a petrol bomb during clashes with pro-European integration protesters in Kiev. Photograph: Stringer/Reuters

The Swedish foreign minister, Carl Bildt, posted on Twitter: "I welcome the announcement in Kiev of talks to resolve the political crisis. But a solution is only possible if there is no regime repression."