Widespread protests against President Viktor Yanukovych’s decision to snub a potentially historic deal with the European Union and focus on ties with Moscow, after immense Russian pressure.

Hundreds of angry Ukrainians clashed with riot police outside the government building on Monday as protests continued in Kiev over the government’s abrupt decision to pause integration with the West and tilt toward Moscow.

Demonstrators called for the government’s ouster, and some of them clashed with riot police, throwing traffic cones and other objects at officers wearing gas masks and armed with rubber batons. The opposition said that one protester was injured.

The scuffle follows a protest in the heart of Kiev on Sunday that was the biggest since the 2004 Orange Revolution that brought a pro-Western government to power. Tens of thousands of people protested against President Viktor Yanukovych’s decision to snub a potentially historic deal with the European Union and focus on ties with Moscow, after immense pressure from Russia.

Mr. Yanukovych’s government suddenly announced last week that it was halting its plans to sign the political association and trade deal with the 28-member EU in order to boost ties with Russia instead, after several years of preparations and firm promises from Mr. Yanukovych that he would sign it.

The government argues the Ukrainian economy would not survive a trade war with Russia, after the Kremlin imposed restrictions on Ukrainian exports, warning Kiev of a possible trade blockade if it goes ahead with the EU deal.

Kiev also blamed the International Monetary Fund for imposing stringent conditions for a bailout loan to aid its struggling economy. Another sticking point was the imprisonment of Mr. Yanukovych’s main foe, former premier and Orange Revolution heroine Yulia Tymoshenko.

Protests continued overnight, with demonstrators camping out in tents on a central square. Round-the-clock rallies are planned for the rest of the week in a bid to urge Mr. Yanukovych to change his mind and sign the agreement at a summit in Lithuania on Friday. But it is unclear how much patience the government will have with the protesters. Prime Minister Mykola Azarov hinted that authorities would not tolerate the kind of 24/7 sit-in that brought Orange Revolution leaders to power in 2004.

Mr. Yanukovych’s office has not commented on the protests, but his ally Mr. Azarov staunchly defended the turn toward Moscow on Sunday evening. In an interview with Ukraine’s ICTV channel, Mr. Azarov snubbed the economic aid offered by the EU as “a pittance” and said that Moscow, by contrast, has offered a discount for Russian natural gas imports, which Ukraine has been seeking for several years.

Dozens of protesters were rallying on European Square in downtown Kiev on Monday morning, dancing to patriotic music blaring from loudspeakers, hiding from rain under umbrellas and waving Ukrainian and EU flags.

“I have been to Europe and seen how people live there. I want my children and grandchildren to have a normal life,” said Halyna Polychuk, 50, a retired store manager who came to Kiev from the western city of Ivano—Frankivsk to join the demonstrations.

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