Activists rally in the center of Kiev, Ukraine, in support of Ukraine's integration with the European Union.
The protest was the biggest Ukraine has seen since the peaceful 2004 Orange Revolution, which overturned a fraudulent presidential election result and brought a Western-leaning government to power.
Led by Ukraine's leading opposition figures carrying giant Ukrainian and EU flags, the demonstrators chanted "Ukraine is Europe" and sang the national anthem as they marched toward European Square.
An estimated 100,000 people turned out for the rally.
"We want to be together with Europe," Volodymyr Mnikh, a 62-year-old retired chemist, said with tears in his eyes.
"We want our children to have a future and not to be pressured by Russia."
Ukraine's leaders announced suddenly last week that they were pulling out of a free trade and political association deal with the EU to be signed in the coming week, saying 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.
"The EU means Ukraine's development," said demonstrator Andriy Mazeta, a 19-year-old management student.
"The Customs Union means Ukraine's destruction. We need to push Russia as far away as possible."
Sunday's protest was seen as a test of the strength of the opposition and its ability to nudge President Viktor Yanukovych back in the EU's direction.
One key EU demand for signing the deal is the release of former Prime Minister Yulia Tymoshenko, whose imprisonment the West sees as politically driven.
Yanukovych only narrowly defeated Tymoshenko in the 2010 presidential election and sees her as a political threat.
He comes up for reelection in 2015.