Ukrainians gathered in the capital Kyiv for a massive protest aimed at denouncing the government of President Viktor Yanukovych and pressuring him into dropping plans for closer ties with Russia.
Hundreds of thousands waved EU and Ukrainian flags as they gathered on Kyiv's Independence Square to protest the government's decision to back away from a trade deal with the European Union in favor of one with Moscow.
In a letter read by her daughter, jailed opposition leader and former prime minister Yulia Tymoshenko said Yanukovych has lost legitimacy as a president, and called for his ouster.
"He [President Viktor Yanukovych] understands only one language. This is the language of peaceful and powerful strength. And we should use it to speak with him. We have to move out him from authority right now," she said.
Earlier, opposition leader Arseniy Yatsenyuk said he would negotiate with President Yanukovych only if he names a new government that will deepen European ties.
The rally comes just days after President Yanukovych met with Russian leader Vladimir Putin for talks on a treaty that the opposition sees as an attempt to recreate the Soviet Union.
Opposition protests erupted late last month, after President Yanukovych refused to sign a long-anticipated EU trade deal. Days later, at an EU summit in Lithuania, German Chancellor Angela Merkel told the Ukrainian leader, "We expected more from you."
Russia has in recent months exerted strong economic pressure on cash-strapped Kyiv to discourage the EU deal. Russia is Ukraine's largest foreign investor, trading partner and chief natural gas supplier.
Moscow is seeking to form a trade bloc of former Soviet republics and satellite countries. Earlier this year, it imposed restrictions on goods from Ukraine, cutting Ukrainian exports 25 percent and dragging the country into recession.
Some information for this report was provided by AP and Reuters.