Kiev, Associated Press—About 10,000 anti-government demonstrators angry about Ukraine’s refusal to sign a pro-European Union agreement converged Saturday on a square outside a monastery where protesters driven away in a pre-dawn clash with police were taking shelter. Some opposition leaders called for nationwide strikes.

The demonstrators outside the St. Michael’s Golden-Domed Monastery were shouting “shame” and “resign.” Opposition leaders at a news conference called on Ukrainians to mobilize en masse.

“Each you have to come out and express your own position on what kind of country you want to live in — a totalitarian, police-controlled country where your children will be beaten up or in a European country,” said Vitaly Klitschko, a world boxing champion and leader of the opposition Udar party.

Klitschko’s call encapsulated the two issues agitating the demonstrators: President Viktor Yanukovych’s refusal to sign an association agreement with the EU and the violent dispersal of protests denouncing that decision.

The association agreement would have established free trade and deepened political cooperation between Ukraine and the EU, but stopped short of membership in the regional bloc.

In the city of Lviv in western Ukraine, where sentiment for European integration is especially strong, 10,000 demonstrators protested the failure to sign on Saturday.

The opposition is calling for Yanukovych to be impeached and on his government to resign. Meanwhile, another prominent protest figure, parliament deputy Arseniy Yatsenyuk, said opposition leaders were working to organize nationwide strikes.

Early Saturday, officers in riot gear moved against several hundred protesters at Independence Square in the Kiev city center, beating some with truncheons. Some protesters then went to the monastery about 500 meters away to take shelter in its cathedral.

In the early morning action, police took 35 demonstrators into custody. Some protesters were bleeding from their heads and arms after the clash.

“It was horrible. We were holding a peaceful demonstration and they attacked us,” protester Lada Tromada said. “They threw us away like garbage.”

Prime Minister Mykola Azarov said in a statement that “the information from different sides which I have at the moment does not allow firm conclusions about who is responsible for this provocation” but said it would be fully investigated.

Kiev police chief Valery Koryak laid the responsibility on the protesters, saying the police were provoked into taking action, the Interfax news agency reported.

A U.S. Embassy statement said “the United States condemns the violence against protesters” and “we urge the government of Ukraine to respect the rights of civil society and the principles of freedom and speech and freedom of assembly.”

About 10,000 people had rallied on the square Friday evening to protest Yanukovych’s backing off from the pact, which had been eagerly anticipated by Ukrainians who want their country to break out of Moscow’s orbit and tilt to the West. Opinion surveys in recent months showed about 45 percent of Ukrainians supporting closer integration with the EU and a third or less favoring closer ties with Russia.

Protests had been held in Kiev over the past week since Yanukovych backed away from the EU agreement. It was to have been signed Friday at an EU summit in the capital of Lithuania, and the passing of that date sparked an especially large turnout of protesters.

Yanukovych argued that Ukraine, a nation of around 45 million, can’t afford to sacrifice trade with Russia. Moscow regards Ukraine as historically part of its orbit and has tried to block the deal with the EU by banning some of Ukraine’s imports and threatening more trade sanctions. A 2009 dispute between Kiev and Moscow on gas prices resulted in a three-week cutoff of gas to Ukraine.

Saturday’s harsh action was in contrast to the mass protests of the 2004 Orange Revolution, when tens of thousands came to the square nightly for weeks and set up a vast tent camp on the main street leading to the square. Police had a mostly low-profile presence during those demonstrations.

Those protests forced the annulment of a fraud-tainted presidential election in which Yanukovych was shown with the most votes. A rerun of the election was ordered and Yanukovych lost to Western-leaning reformist Viktor Yushchenko.

Yanukovych was elected president five years later, narrowly defeating then-Prime Minister Yulia Tymoshenko, the leading figure of the Orange Revolution.

Tymoshenko was sentenced to seven years imprisonment in 2011 for abuse of office, a case that the West has widely criticized as political revenge. The EU had set Tymoshenko’s release, or at least her freedom to go to Germany for treatment of a severe back problem, as a key criterion for signing the association pact with Ukraine.

The prospect of freeing his archenemy was deeply unattractive to Yanukovych.

Tymoshenko’s daughter Eugenia read a statement from her mother to the crowd outside the monastery calling on Ukrainians to demonstrate “against the dictatorship and violence of Yanukovych.”