Ukrainian Prime Minister Mykola Azarov says protests in Kyiv and other cities in the country have "all the signs of a coup d'etat."
Azarov made the comment on December 2 during a meeting with foreign ambassadors in Kyiv, adding, "From a mass protest, this has grown into one that is out of control."
Hundreds of thousands of demonstrators have turned out in Kyiv and other Ukrainian cities, pushing for the resignation of the government of President Viktor Yanukovych over his refusal to sign an Association Agreement with the European Union and seek better ties with neighbor Russia
Protesters on December 2 blocked access to the government headquarters, while others continued to occupy city hall and the central labor-union building.
Former Interior Minister and now opposition leader Yuriy Lutsenko vowed the protests will continue. "The Cabinet of Ministers must go away, and a new life, as well as an economic [life], must start," he said.
The besieging of the government headquarters follows a rally of hundreds of thousands in Kyiv on December 1. Estimates put the number of protesters in Independence Square at more than 100,000 and possibly up to 500,000.
It was the biggest demonstration in the Ukrainian capital since the 2004-05 Orange Revolution.
There were clashes between protesters and police near the city's presidential administration building, where police used tear gas and truncheons to drive away the protesters.
More than 200 people -- both civilians and police -- were reported hurt during the clashes. Ukrainian and foreign journalists were among those injured. The opposition has blamed the violence on "provocateurs."
WATCH: Ukrainian protesters besiege the government building.
Hundreds of protesters spent the night in a tent camp on Independence Square, where they were being joined by others on December 2. One of the protesters said: "I'll stay until the end. I have nothing to lose. I have a granddaughter. I have adult children. At least let them have a good life."
Protesters also holed up overnight in Kyiv's city hall and the central union building, which they had stormed on December 1.
There were reports of protests by thousands in other Ukrainian cities as well. In the western city of Lviv, more than 40,000 demonstrated on December 1.
A spokesman for Prime Minister Azarov, Vitaliy Lukyanenko, denied reports the government was considering introducing a state of emergency.
The opposition has called for a general strike and wants to oust the government in a confidence vote in parliament on December 3.
The European Commission, the EU's executive arm, has called on both sides to show restraint.
European Commission President Jose Manuel Barroso voiced concern, and called for restraint on December 2.
"We are following with great attention and concern the developments in Ukraine. We have already said very clearly that Ukraine authorities should respect, of course, democratic freedoms and the right of people to demonstrate," Barroso said.
"At the same time, we have made an appeal to demonstrators to show restraint. Of course, this comes as a result of the fact that many, many Ukrainians see their future in Europe and they are disappointed with the result of the Vilnius [EU Eastern Partnership] summit."
The European Commission said that in a telephone call with Barroso on December 2, Yanukovych had asked the commission to receive a Ukrainian delegation to discuss some aspects of the Association Agreement.
Barroso told him the commission "stands ready to discuss aspects of implementation related to the agreements already initialed, but not to reopen any kind of negotiations."
Some opposition leaders have also called for EU sanctions against Yanukovych, but an EU spokeswoman said no sanctions were being considered at this moment.
The U.S. ambassador to Ukraine, Geoffrey Pyatt, said, "What happened Saturday cannot be swept under the carpet." He also said the U.S. policy of engagement with Kyiv had not changed.
Putin: 'More Like A Pogrom Than A Revolution'
In Yerevan, on a visit to the Armenian capital, Russian President Vladimir Putin likened the protests in Ukraine to a "pogrom."
He said the demonstrations "remind me more of pogroms than a revolution. Regardless of how odd it may seem, I believe, it has little to do with Ukraine's relations with the European Union."
"Let me point out one thing -- nobody is bothering to have an in-depth look at the drafts of these agreements [with the EU]. See nothing, hear nothing. They are saying that a dream is being snatched from the Ukrainian people," Putin continued.
"However, a close look at these [EU] agreements shows that lots of folks may simply not live long enough to live that dream -- and it's not a bad dream as a matter of fact -- they may not make it there. It's because the conditions [of EU membership] are very tough."
Protests against Yanukovych's decision to back out of signing an Association Agreement with the EU were galvanized by a violent police crackdown on November 30.
Ukraine was supposed to sign an Association Agreement with the EU at a summit in Vilnius at the end of November, but the government suddenly announced it was suspending efforts toward signing the document about a week before the conference.
Yanukovych justified his turnabout just days before the summit by saying that Ukraine could not afford to break trade ties with Russia.
Russia had threatened trade reprecussions if Ukraine signed the agreement.
With reporting by Reuters, ITAR-TASS, Interfax, AP, dpa, and RFE/RL Brussels correspondent Rikard Jozwiak