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A shaky truce crumbled Thursday as gunfire erupted at Independence Square, the center of anti-government protests and an increasingly violent crisis that protest leaders say left as many as 128 dead in recent days.

Fires burn as protesters and security forces clash in Kiev, Ukraine Tuesday night, February 18, 2014. (Credit: Courtesy Freki Films)

At least 100 people have died and 500 have been injured since Thursday morning, the head of the protesters’ medical service told CNN.

The Ukrainian government has not released an updated figure, but the interior ministry said earlier that one police officer was among the dead.

It’s unclear what prompted the gunfire just hours after the government declared a truce. But 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.

“Protesters broke the truce,” said a statement from President Viktor Yanukovych’s office.”The opposition used the negotiation period to buy time, to mobilize and get weapons to protesters.”

When the bullets flew, several demonstrators fell to the ground.

Protesters grabbed the wounded by their clothes or limbs, and carried many of them to a hotel lobby at one end of the square that had been converted into a triage center.

Bodies, covered in bloodied sheets, lay on the floor. Orthodox priests prayed over them.

Protest medical volunteer 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.

On Tuesday, 28 people — protesters and police — were killed, officials said.

If Thursday’s death toll is confirmed, it would make it the deadliest day of the protests, which began in November when Yanukovych reversed a decision to sign a trade deal with the European Union and instead turned toward Russia.

Diplomatic efforts under way

Beyond Kiev’s chaotic center, European Union officials were scheduled to meet Thursday in an urgent session to discuss possible sanctions against the Ukrainian government, which could include freezing assets and restricting the visas of officials deemed responsible for violence in that country, French Foreign Minister Laurent Fabius said on Twitter.

He was in Ukraine’s capital Thursday, along with foreign ministers from Germany and Poland, meeting with various opposition leaders and Yanukovych ahead of the emergency session in Brussels.

German Chancellor Angela Merkel urged the Ukrainian President to accept European help in talks with the anti-government opposition, Merkel’s office said Thursday.

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.

As the protests continued, anger over the rejected trade deal with the EU morphed into resentment of Yanukovych, his closeness to Russia, and the power he wields.

The violence caused political fallout in the President’s own party and elsewhere.

Kiev Mayor Volodymyr Makeenko announced his resignation from office and the country’s ruling party, according to the city administration website. The same post also announced that the city’s metro transit system is reopening.

At the Sochi Olympics, Ukrainian athletes wearing black mourning bands held a moment of silence Thursday for fellow citizens slain in the violence erupting in Kiev, the Ukrainian Olympic committee said.

Thursday’s violent developments came just hours after Yanukovych announced a truce — and opposition leaders agreed to abide by it.

Opposition leader Vitali Klitschko, a former world-class boxer, met with Yanukovych Wednesday — discussions that led to the truce. He was expected to sit down with the President Thursday as well, but after the latest violence and deaths, it’s not clear if the meeting will still take place.

Senior officials in U.S. President Barack Obama’s administration told CNN Wednesday they were bracing for Ukraine to intensify its crackdown under pressure from Russia.

“Things have gotten very bad,” one official said. “The government is speaking in very nasty, aggressive and confrontational terms. It signals they are prepared to do something.”

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.”