Shrouded in smoke and tear gas and echoing with the din of stun grenades and drums, the center of Kiev turned into a battle zone amid deadly clashes between security forces and protesters.

Police launched the first assault against stone-throwing protesters in the morning, marching forward as a military formation clad in body armor with their shields in front.

Ukrainian police on Wednesday stormed protesters' barricades in Kiev amid violent clashes that left five activists dead, the first fatalities in two months of anti-government protests.

Pitched battles raged in the center of the Ukrainian capital as protesters hurled stones and Molotov cocktails at police and the security forces responded with tear gas, stun grenades and rubber bullets.

The Ukrainian authorities will have no choice other than to use force against protests if "provocateurs" do not stop inciting clashes, Prime Minister Mykola Azarov said Tuesday.

"If the provocateurs do not stop then the authorities will have no choice other than to use the force set out under the law and ensure the security of our people," he told Russia's Vesti 24 state news channel in an interview, referring to controversial anti-protest laws that came into force Tuesday.

Two months since the first protests erupted in Ukraine over the government's rejection of an EU pact, the protest movement has radicalized as impatience grows with the inability of opposition leaders to bring about change.

Demonstrators are still occupying Independence Square in central Kiev, known locally as the Maidan and the center of the 2004 Orange Revolution, where a vast tent city has sprouted up.

Ukrainian protesters and security forces on Tuesday refrained from using further force after two days of clashes but an uneasy standoff remained with neither side giving way.

After a night of violence, a temporary truce appeared to be in place with the protesters no longer launching the Molotov cocktails and stones that had marked their action since the clashes erupted on the night of January 19.

At least 35 reporters have been wounded in the clashes between security forces and protesters in Kiev over the last days, a Ukrainian media rights group said Tuesday, with two journalists who were detained saying they were beaten by police.

Ukrainian press freedom group the Institute of Mass Information listed the names of 35 reporters hurt since the clashes broke out on Sunday.

Russia on Tuesday warned the situation in Ukraine was spiraling out of control after a second night of violent clashes between pro-EU protesters and security forces in the center of Kiev.

The clashes raged in the center of the Ukrainian capital until early morning Tuesday, with demonstrators flinging Molotov cocktails and stones at security forces who hit back with stun grenades, rubber bullets and tear gas.

In normal times, Grushevsky Street is one of the nicest avenues in Ukraine's capital Kiev. But now its cobble stones have been ripped out by demonstrators to use as weapons in their standoff with police.

Separated by twenty meters (yards) of no-man's land and protected by meters-high barricades, protesters and the Ukranian security forces are engaged in a pitched battle that has turned an area in the center of Kiev into a virtual warzone.

Ukrainian President Viktor Yanukovych said on Monday that clashes between police and protesters in the capital Kiev threatened the entire country, as he made a call for dialogue.

"I am convinced that such phenomena are a threat not only to the public in Kiev but all of Ukraine," Yanukovych said in an address to the nation published on the presidential website.

Ukraine's Prosecutor General Viktor Pshonka on Monday warned protesters to halt "mass rioting" in Kiev, describing it as a crime against the state.

"It is necessary to immediately halt the mass rioting which bears a threat to state security. It is not just hooliganism. It is a crime against the state," he said in a statement, calling on opposition leaders to halt the clashes between protesters and police.