violence and paving the way for peaceful, long-term political solutions.
Such attempts have been tried in the three months since protesters began occupying Kiev's Maidan, or Independence Square. But they have gone nowhere, including two truces that ended suddenly, and bloodily, in the past week.
The latest bloodshed happened early Thursday, a mere hours after Ukraine's president and the leaders of three opposition parties agreed to a truce and talks.
Pitched battles broke out in downtown Kiev, with protesters tossing rocks and firebombs at police under a sky blackened by smoke from their burning barricades. At least one protester fired toward police lines with a shotgun.
Security forces appeared to fight back with automatic weapons and at least one sniper rifle.
In video shot by Radio Free Europe, men wearing what appear to be government uniforms fired at unseen targets with automatic rifles and a sniper rifle with a telescopic sight. CNN could not immediately confirm their target.
In another video shot by CNN, a medic trying to help a man on the ground is felled by gunfire.
In all, more than 100 people died in the fighting Thursday, protest medical officials said. The government didn't release its own figures. Regardless, any figure would easily top the death toll at least 26 from Tuesday and make Thursday the bloodiest day in this unrest.
"I'm cleaning blood from the floor and I'm crying because this is really hard for me," said a man named Anton, who was volunteering at a protest medical clinic set up in a hotel.
In a statement that appeared to increase pressure on protesters, the Interior Ministry said it reserved the right to use force to free about 70 police officers it said had been taken hostage Thursday by protesters.
However, a number of people purporting to be police officers appeared on Ukrainian television saying they had joined protesters of their own free will. It wasn't clear whether those claiming to be police officers were among those allegedly taken hostage.
The European Union said it would freeze the assets of Ukrainians deemed responsible for the violence, with the United States adding that it was rushing to impose sanctions of its own.
"There is widespread horror in the European Union as well as in the United Kingdom at the scale of the loss of innocent life and the events of the last 48 hours," British Foreign Minister William Hague said.
Meanwhile, Russia said it would send a mediator to try to ease the crisis, even as its United Nations ambassador accused protesters of trying to overthrow Ukraine's President and other officials accused the West of meddling in its neighbor's sovereign affairs.
Thursday's violence broke out just hours after the government announced a truce in the fighting, which at that time had drawn international reproach following Tuesday's clashes between government forces and protesters.
CNN crews at the scene reported that as security forces were moving away from the area, a group of protesters pursued them throwing rocks and Molotov cocktails.
Interior Minister Vitali Zakharchenko said the violence had been "provoked exclusively by the opposition leaders," echoing an earlier statement from President Viktor Yanukovych's office accusing protesters of breaking the truce.
"The opposition used the negotiation period to buy time, to mobilize and get weapons to protesters," the statement from the President's office said.
However, a doctor volunteering to treat protesters, Olga Bogomolets, accused government forces of shooting to kill, saying she had treated 13 people she believed had been targeted by "professional snipers."
"They were shot directly to their hearts, their brain and to their neck," she said. "They didn't give any chance to doctors, for us, to save lives."
CNN could not independently confirm Bogomolets' claim of sniper fire.
At the hotel converted into a triage center, bodies covered in bloodied sheets lay on the floor. Orthodox priests prayed over them.
Kiev Mayor Volodymyr Makeenko announced his resignation from the country's ruling party and reopened the city's mass transit system -- which government officials had shut down to prevent protesters from reaching central Kiev's Independence Square, also known as the Maidan.
At the Sochi Olympics, Ukrainian athletes held a moment of silence Thursday for fellow citizens slain in the violence, the Ukrainian Olympic committee said.
Roots of the crisis
The violence inflames a crisis that started in November, when Yanukovych reversed a decision to sign a trade deal with the European Union and instead turned toward Russia.
Ukraine's population has long been divided between historic loyalties to Europe and its eastern neighbor.
Western foreign ministers were in Kiev Thursday trying to find a solution, and Russia said it will send a mediator there at Yanukovych's request to negotiate with the opposition.
But the Russian ambassador to the U.N., Vitaly Churkin, said his government doesn't believe the opposition wants a dialogue. He accused protest leaders of invading government facilities as a buildup to a takeover of parliament.
"We think that this attempt to execute a violent coup should stop," he said.
In a statement, the White House said it was outraged by images of security forces firing on protesters and urged those forces to withdraw and "respect the right of peaceful protest."
Diplomatic efforts under way
After meeting in urgent session in Brussels, European Union officials agreed to freeze the assets of Ukrainians deemed responsible for the violence, and to prevent them from traveling into the European Union, the organization said in a statement.
The United States was also preparing an order to freeze assets of Ukrainians who are believed to be involved in the crackdown, a senior administration official said Thursday.
It's likely President Barack Obama will sign the order later in the day, but his administration is closely watching diplomatic efforts on the ground to make sure such a move won't be counterproductive, the administration official said.
The foreign ministers of Germany, France and Poland traveled to Kiev on Thursday to meet with opposition leaders and Yanukovych. They had planned to attend the Brussels meeting, but talks went longer than expected, a German foreign ministry spokeswoman told CNN.
Late Thursday, Polish Foreign Minister Radoslaw Sikorski said via Twitter that the hourslong talks involving all sides had led to some "progress ... but important differences remain."
German Chancellor Angela Merkel -- who also talked Thursday about the situation with Obama -- urged the Ukrainian President to accept European help in talks with the anti-government opposition, Merkel's office said Thursday.
But it appeared Yanukovych was holding fast to his Russian allies. On Thursday, Russian President Vladimir Putin's spokesman said the country was sending its human rights ombudsman to negotiate with the opposition at Yanukovych's request.
Russia's foreign ministry appeared to criticize Western diplomatic efforts, according to a report by Russian state news agency RIA Novosti.
"The ongoing attempts to obtrusively intervene from outside, threat with sanctions or trying to influence the situation in any other ways are inappropriate and can't lead to anything good but can only aggravate the confrontation," the report quoted spokesman Aleksandr Lukashevich.
Analysts warned there was little that outside pressure could do, especially if the Ukrainian military gets involved on the side of the government cracking down on protesters.
"My own hunch," said Council on Foreign Relations President Richard Haass, "is this is going to continue to escalate."