KIEV — About 50,000 demonstrators rallied in the center of Kiev on Sunday to demand that Ukraine’s government reverse course and sign a landmark agreement with the European Union in defiance of Russia.
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.
The rally was led by Ukraine’s top opposition figures, who called for the protests to continue until President Viktor Yanukovych agreed to sign the free trade and political association deal with the EU at a summit on Friday.
As during the Orange Revolution, the opposition set up tents and encouraged supporters to spend the night. It was unclear how many would stay, with temperatures in the 40s and rain forecast.
Sunday’s demonstration was sparked by anger over the government’s sudden move last week to pull out of the EU agreement and focus instead on trade ties with Russia, under strong pressure from Moscow.
After the rally at European Square, dozens of protesters clashed with police and pro-Russia activists near the government building, while another standoff took place outside Yanukovych’s office. Police said they used tear gas at the government building after protesters threw a smoke bomb and refused to back off.
A larger crowd of several thousand headed for nearby Independence Square, planning to continue the protest. Meanwhile, Yanukovych supporters held their own rally on another Kiev square.
The pro-EU demonstrators, carrying giant Ukrainian and EU flags, chanted ‘‘Ukraine is Europe’’ and sang the national anthem as they marched toward European Square for the rally.
“Should we go toward Europe or toward Russia? It’s a choice between the past and the future,” opposition leader Arseniy Yatsenyuk, a top ally of Yulia Tymoshenko, imprisoned former prime minister, told the crowd.