WASHINGTON, Dec. 2 -- The U.S. urged Ukraine's leaders to respect people's right of free speech on Monday, saying that violence against demonstrators in Kiev was "unacceptable".

"The violence by government authorities against peaceful demonstrators in Kiev on Saturday morning was unacceptable," said White House Spokesman Jay Carney.

Massive demonstrations rocked the Ukrainian capital of Kiev, with tens of thousands of people taking to the streets over the weekend to protest against President Viktor Yanukovych's decision to suspend a trade pact with the European Union (EU).

Thousands of demonstrators stormed the presidential administrative building and the office of the mayor of Kiev, leading to violent clashes between police and protesters and leaving 53 demonstrators injured, according to the Kiev administration healthcare department.

"We urge Ukraine's leaders to respect their people's right to freedom of expression and assembly," Carney said at White House's daily press conference, adding that the U.S. does not consider these demonstrations coup attempts.

Sunday's protest was reportedly the largest since rally began on Nov. 21, when Ukraine, which was due to sign political-economic agreements with the EU at the Eastern Partnership Summit held in Lithuania on Nov. 28-29, suddenly announced to put the deal on hold, opting for closer trade ties with Russia instead.

"We continue to support the aspirations of the Ukrainian people to achieve a prosperous European democracy. European integration is the surest course to economic growth and to strengthening Ukraine's democracy," Carney said.