Thousands of defiant protesters faced rows of riot police who have squeezed them deeper into Kiev's Independence Square which has been a bastion and symbol for the protesters after clashes that set buildings on fire and brought sharp rebuke from both the West and Russia.
The violence on Tuesday night was the worst in nearly three months of anti-government protests that have paralysed Ukraine's capital in a struggle over the identity of a nation divided in loyalties between Russia and the West and the worst in the country's post-Soviet history.
The Kremlin said it had put the next part of its bailout on hold amid uncertainty over Ukraine's future and what it described as a "coup attempt"; it criticised the West for the escalation of violence.
President Viktor Yanukovych blamed the protesters for the violence and said the opposition leaders "crossed a line when they called people to arms".
The EU appears poised to impose sanctions as it called an extraordinary meeting of the 28-nation bloc's foreign ministers today.
European Commission president Jose Manuel Barroso called for "targeted measures against those responsible for violence and use of excessive force can be agreed ... as a matter of urgency".
Sanctions would at first typically include banning leading officials from travelling to the 28-nation bloc and freezing their assets there.
Mr Barroso added: "It is the political leadership of the country that has a responsibility to ensure the necessary protection of fundamental rights and freedoms. It was with shock and utter dismay that we have been watching developments over the last 24 hours in Ukraine."
French president Francois Hollande said those who have caused the deadly violence in Ukraine "will be sanctioned" and called the violence "unqualifiable, inadmissible, untolerable acts".
The US urged the Ukrainian government to pull back riot police from Independence Square, call a truce and hold discussions with the opposition.
White House Deputy National Security Adviser Ben Rhodes said the White House would consider the use of sanctions against those responsible for the violence in Ukraine and was in consultation with the EU about possible sanctions.
He said the US would also like to see Russia support efforts to reduce tensions in Ukraine.
The protests began in late November after Mr Yanukovych turned away from a long-anticipated deal with the EU in exchange for a multi-billion bailout from Russia.
The centre of Kiev was cordoned off by police yesterday morning, the subway was shut down and most shops on Kiev's main street were closed.
But hundreds of Ukrainians still flocked to the opposition camp, some wearing balaclavas and armed with bats, others carrying food to protesters who later seized control of the main post office.
Meanwhile, in the western Ukrainian city of Lviv, where most residents yearn for stronger ties with the EU and have little sympathy for Mr Yanukovych, protesters seized several government buildings, including the governor's office, police stations, prosecutors and security agency offices and the tax agency headquarters.
They also broke into an interior ministry unit and set it on fire. Some protesters were driving around town in police cars they had seized during the night.
The government imposed restrictions on transport moving towards Kiev, apparently to prevent more opposition activists from coming from the Western part of the country, and at least one train from Lviv was held outside Kiev.