Ukrainian opposition leaders are vowing to press ahead with protests against the president despite the violent dispersal of demonstrators during the night.

Police swinging truncheons waded into a crowd of about 400 protesters early Saturday on the capital's Independence Square and took 35 demonstrators into custody. Some protesters were bleeding from their heads and arms after the clash.

About 10,000 people had rallied on the square Friday evening to protest President Viktor Yanukovych's refusal to sign an association agreement with the European Union and speakers called for another mass gathering on Sunday.

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

Opposition parliament member Oleksandra Kuzhel was quoted by the Interfax news agency on Saturday as saying "We don't intend to step back" and will try for another protest on Sunday.

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."

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.

Another opposition leader, Arseniy Yatsenyuk, said that after the events of the last day "we awoke in a new country. Ukraine after Vilnius is more like Belarus," the authoritarian former Soviet republic to the north, according to Interfax.

Yanukovych abruptly changed course for integration with the EU last week. The move angered many in Ukraine, where nearly half of the population of around 45 million favors closer ties with the EU.

Yanukovych argued that Ukraine can't afford to sacrifice trade with Russia, which regards Ukraine as historically part of its orbit and has tried to block the deal 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 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.