Several thousand people have gathered in Kyiv's Independence Square demanding the government reverse its position on European integration.
Some 3,000 people turned out on the evening of Novermber 22 in Kyiv to express their dissatisfaction with the government's decision the previous day to suspend talks with the European Union on signing an Association Agreement.
Some minor clashes with police were reported.
Opposition leader Vitali Klitschko was among the demonstrators in Kyiv and said the crowd wants Ukraine's government to sign the agreement at an EU Eastern Partnership summit in Vilnius next week.
Similar demonstrations were held in other cities around the country. In the western city of Lviv, several thousand people protested, chanting "Glory to Ukraine."
The city's mayor, Andriy Sadoviy, said demonstrators still hope to pressure the government to sign the agreement at the Vilnius summit.
"The state has to sign the Association Agreement in Vilnius," Sadoviy said. "And these young people, they will stand here until the end because this is our only chance. We want to be a free country. We know very well how it was to be in that (Soviet) Union. That's why we want to have normal European civilized values, and people will stand for this until the end."
EU Enlargement Commissioner Stefan Fuele said in Brussels on November 22 that it is still possible the agreement could be signed in Vilnius.
"No, we have not fully given up as we were not actually officially informed by the Ukrainian side that this signature is impossible at Vilnius," Fuele said. "We are of course aware of what the president had to tell me when I met him on (November 19). We are of course aware of the government's decision; we are of course aware of the president's prerogative to conclude and sign the international treaties and between now and the Vilnius summit there are still a couple of days."
Speaking on television on November 22, Prime Minister Mykola Azarov said he sees "absolutely no tragedy" in putting off the agreement for six months. He emphasized that Ukraine cannot afford to see its trade with Russia cut and said the EU had not offered sufficient compensation.
Azarov denied that Kyiv made the decision under pressure from Russia.
In Washington, U.S. Secretary of State John Kerry said that he would not attend a December meeting of the Organization for Security and Cooperation in Europe (OSCE) that will be held in Ukraine. He cited scheduling conflicts.
U.S. Vice President Joe Biden spoke with Ukrainian President Viktor Yanukovych by telephone, expressing Washington's "disappointment" with Ukraine's decision.
(Based on reporting by Interfax and AP)