Tens of thousands of demonstrators marched through Kiev on Sunday to demand the government reverse course and sign a landmark agreement with the EU.
However, some protesters tried to storm government buildings and police responded by using tear gas and batons against the demonstrators.
The protest was the biggest the country has seen since the peaceful 2004 Orange Revolution, which overturned a fraudulent presidential election result and brought a Western-leaning government to power.
Ukrainian and EU flag-carrying demonstrators shouted "Ukraine is Europe" and sang the national anthem as they marched towards Independence Square.
The protest was led by Ukraine's top opposition figures, who called for the rallies to continue until President Viktor Yanukovych agreed to sign the free trade and political association deal with the EU at a summit on Friday.
Pro-Europe supporter Anton Vashkevich said the protesters wanted to say that the government and President did not represent the opinion of the whole country.
Tymoshenko release demand
"What they think does not express the thoughts of the majority of the population," Vashkevich said.
"There is no alternative to the European Union."
Ukraine's leaders announced suddenly last week that they were pulling out of the EU agreement because they said the country could not afford to break trade ties with Russia.
The Russian government has worked aggressively to derail the EU deal and bring Ukraine into the Moscow-dominated Customs Union.
One key EU demand for signing the deal was the release of former Prime Minister Yulia Tymoshenko, whose imprisonment the West sees as politically driven.
Tymoshenko's daughter Eugenia was one of those attending Sunday's protest march.
Elsewhere in Kiev, thousands of Yanukovych supporters held their own rally on Sunday.
Those attending the march came to voice their support for the government's decision to halt the signing of the EU agreement.
One government supporter, Nina Gorkava, said that the EU was not offering Ukrainians anything and was just putting a heavy burden on them.
"Why should we follow their rules? If we voted for independence of our country we should be really independent," she said.
The EU has said that Yanukovych is still welcome to attend the summit in Vilnius, Lithuania, on Thursday and Friday, during which the two sides had intended to sign the trade agreement.
Source: Al Jazeera