Ukranian President Viktor Yanukovich has vowed that the authorities would never use force against peaceful protests, and urged the opposition to sit down for talks.
"For the sake of achieving compromise I am calling on the opposition not to reject [talks], not to follow the path of confrontation and ultimatums," Yanukovich said in a statement on Wednesday.
But the opposition, which earlier ruled out any negotiations until he dismissed the government and punished riot police for crushing a smaller protest on November 30, vowed to do everything to topple the president.
The capital has been gripped by more than three weeks of demonstrations against Yanukovich's decision to align himself with Russia instead of the European Union.
Several dozen people were injured in the early hours of Wednesday when riot police and interior ministry special forces moved against the demonstrators who have occupied Kiev's Independence Square.
The security forces tore down makeshift barricades but were eventually forced into a retreat amid cheers from the demonstrators after the ranks of protesters swelled.
"With what happened last night, Yanukovich closed off the path to any kind of compromise," opposition leader Vitaly Klitschko told a news conference, adding that they "had planned to have talks with Yanukovich. We understand that Yanukovich has no wish to talk to the people and only understands physical force, which he uses against the protesters."
Jailed former Prime Minister Yulia Tymoshenko earlier on Wednesday warned the protest movement against holding any negotiations with Yanukovich.
"I am calling on all Ukrainians: rise up!" Yanukovich's arch rival said in a statement. "No talks with the gang."
This response is neither acceptable nor does it befit a democracy.
Yanukovich's refusal to sign an EU trade deal prompted the country's largest street demonstrations since the 2004 Orange Revolution, which successfully overturned the results of a vote allegedly marred by massive corruption.
Hundreds of thousands of people marched this past weekend, the second in a row that such huge crowds have vented fury at a government they accuse of returning the country to Kremlin control.
Yanukovich had called on Tuesday for the release of demonstrators arrested in the massive protests and vowed that Ukraine was still interested in integrating with Europe, but stopped far short of opposition demands that his government resign.
Riot police have twice previously dispersed demonstrators with clubs and tear gas, beating some severely enough to send them to intensive care.
US Secretary of State John Kerry issued a strong statement on Wednesday, expressing the United States' "disgust with the decision of Ukrainian authorities to meet the peaceful protest ... with riot police, bulldozers, and batons, rather than with respect for democratic rights and human dignity."
"This response is neither acceptable nor does it befit a democracy," said Kerry, urging authorities to show "utmost restraint" and protect human life.
In Washington, the State Department said the US was considering "a range of options" to respond to Ukraine's protest crackdown, including possible sanctions.
EU foreign policy chief Catherine Ashton met Yanukovich twice over the past two days and US Assistant Secretary of State Victoria Nuland told the president the attempted police crackdown was "inadmissable".
An estimated 5,000 pro-EU demonstrators were camping out in Independence Square on Wednesday night, reinforcing barricades with snow and sand bags.