Ukrainian President Viktor Yanukovych on Thursday demanded an extraordinary session of parliament to ease the crisis in the country after five days of deadly clashes between protesters and security forces.

The three main opposition leaders were to hold crisis talks with Yanukovych, as world boxing champion and UDAR (Punch) party leader Vitali Klitschko brokered a truce in the violence between protesters and police.

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.

The United States has revoked the visas of several Ukrainian nationals linked to the latest outbreak of violence in Kiev, the U.S. embassy in Kiev said Wednesday after two protesters were killed during clashes with police.

"In response to actions taken against protesters on the Maidan in November and December of last year, the U.S. Embassy has revoked the visas of several Ukrainians who were linked to the violence," the embassy said in a statement, without naming the individuals.

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.

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.

Opposition protesters were Monday locked in a tense standoff with Ukrainian police in Kiev after bloody clashes that wounded over 200 people, as President Viktor Yanukovych called emergency talks to resolve the crisis.

The clashes, the worst in Kiev in recent times, came amid mounting anger over laws restricting protests signed by Yanukovych after almost two months of demonstrations against his refusal to sign a pact for integration with the EU.

Ukraine's ex-interior minister turned opposition leader Yuriy Lutsenko was in intensive care in hospital Saturday after being beaten in fresh clashes between pro-EU demonstrators and club-wielding police.

A few hundred nationalist demonstrators protested late Friday outside a Kiev court that had earlier in the day sentenced three men to six years in prison for allegedly plotting to blow up a statue of Soviet founder Lenin near the city's main airport in 2011.

A Ukrainian court on Friday launched highly-charged hearings against jailed opposition leader Yulia Tymoshenko's attorney that government critics have branded a political show trial.

Former prime minister Tymoshenko's lawyer Sergiy Vlasenko is accused by his former wife of domestic violence -- a case that emerged in November just as Ukraine was deciding whether to sign a historic agreement with the European Union.

Unknown assailants have savagely beaten a dogged Ukrainian journalist who has taken part in pro-EU rallies, triggering outrage among the opposition locked in a confrontation with President Viktor Yanukovych.

Tetyana Chornovil, who writes for the Ukrainska Pravda opposition website, was attacked overnight Tuesday outside the capital Kiev, police said in a statement, citing the journalist.

Ukraine has banned entry to former Georgian president Mikheil Saakashvili and 35 other foreigners suspected of working with the opposition "to destabilize" the country amid mass pro-EU protests, a report said Tuesday.

The Ukrainian foreign ministry and the security service have declared Saakashvili, 29 other Georgians, five US citizens and one Serb as persona non grata, the Kommersant Ukraine daily reported.