Right wing protesters practice defense skills on the Mikhaylivska Square in downtown Kiev, Ukraine, on Saturday. (FILIP SINGER/EPA)

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.

Opposition leaders called for nationwide strikes and for Ukrainians to mobilize en masse. Another big demonstration was planned for Sunday.

The demonstrators outside the St. Michael’s Golden-Domed Monastery shouted “Shame!” and “Resign!” As temperatures hovered just above freezing, some vowed to spend the night on the square.

“Each of you has 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 a European country,” said Vitaly Klitschko, a world boxing champion and leader of the opposition UDAR party.

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

Yanukovych said in an address Saturday evening that he condemned “the actions that led to the forceful confrontation and the suffering of people.” He called for an investigation and for those responsible to be punished.

“I confirm that we are united in our choice of a common European future,” he said. Yanukovych has said that he hopes Ukraine will one day sign the agreement with the E.U. but that the country cannot at present afford to sacrifice trade with Russia.

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

In the western city of Lviv, where sentiment in favor of European integration is especially strong, about 10,000 people protested the failure to sign.

Meanwhile, parliament deputy Arseniy Yatsenyuk called for Yanukovych to be impeached and urged his government to resign. 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 yards away to take shelter in its cathedral.

In the early-morning action, police took 35 demonstrators into custody.

The U.S. State Department and the E.U. condemned the violence against the protesters.

“We urge Ukraine’s leaders to respect their people’s right to freedom of expression and assembly,” State Department spokeswoman Jen Psaki said in a statement.

— Associated Press