Ukraine's opposition hoped Sunday to muster a million-strong rally in a new push to wring concessions from President Viktor Yanukovych in a bitter confrontation over a rejected EU pact.
Yanukovych's decision to drop political and free trade agreements with the EU in favour of tighter Russian ties and a crackdown on an opposition rally plunged the ex-Soviet nation into its worst political crisis in a decade.
The president incensed the opposition and its supporters further by discussing the signing of a strategic partnership treaty with Russian President Vladimir Putin at the Black Sea resort of Sochi on Friday.
Opposition leaders said Saturday that they would not sit down for talks with Yanukovych unless he dismissed the government, released arrested protesters and punished riot police officers for crushing an opposition rally last week.
"This is an ultimatum of the Ukrainian people and not just the opposition," said Arseniy Yatsenyuk, leader of Batkivshchyna (Fatherland) party.
The protests in Ukraine have raged for over two weeks after the government abruptly announced it was halting the work on the agreements with the European Union.
Last Sunday, hundreds of thousands took to the streets in Kiev and pro-EU western Ukraine in the largest demonstrations since the pro-democracy Orange Revolution in 2004 forced the annulment of fraud-tainted elections initially claimed by Yanukovych.
The rally in Kiev descended into unprecedented clashes with riot police in which hundreds were injured.
Boxing champion turned opposition leader Vitali Klitschko said a million should take to the streets of Kiev on Sunday.
"Our future depends on you," the pugilist said.
Yanukovych, who faces an election in 2015, has promised a thorough investigation into the use of force against the protesters but has not said whether he is ready to sit down for talks with the opposition.
In a sign of mounting pressure, he postponed a trip to Malta planned for next week.
Putin has slammed the protests, saying they looked more "like a pogrom than a revolution."
In contrast, the West has urged the Ukrainian authorities to heed the demands of the protest movement.
Protesters have seized control of Kiev's iconic Independence Square, setting up a tent city amid barricades and blockading several public buildings.
In a sign of further tensions, the authorities said Saturday they had deployed riot police outside the offices of the public broadcaster.
Interior Minister Vitali Zakharchenko, in a statement early Sunday, called on protesters to respect the law and said police were ready to cooperate.
Elmar Brok, chairman of the European Parliament's foreign affairs committee, said during a visit to Kiev on Saturday that the bloc may introduce travel bans against those responsible for the use of violence against the protesters.
"Aggression should be punished," he told reporters.
"If this does not happen, if they are not punished, then all those who are responsible for the work of law enforcement agencies in that situation will not have an opportunity to come to the EU."
Jailed opposition leader Yulia Tymoshenko, who had hoped to walk out of prison as a result of the EU deal, has called on the West to impose sanctions against Yanukovych and his family including his son Olexander, one of the country's richest men.
Economists have said the protests risk exacerbating an already serious economic crisis and causing a crash in the value of its currency.
The Ukrainian government rejected the pact with the EU, citing Russian threats of sanctions and the EU's failure to deliver financial support.
Analysts believe Russia offered Ukraine cheaper natural gas and billions of dollars in aid in exchange for joining a Moscow-led customs union.
The Economist's senior editor Edward Lucas, citing sources, tweeted that during the Friday talks Yanukovych had promised Putin to join the customs union by 2015 in return for aid.
Both Ukrainian and Russian authorities said no deal was signed in Sochi.