Ukraine launched an offensive against separatist forces for control of the besieged eastern Ukrainian city of Slovyansk on Friday, while clashes between pro- and anti-government activists in the previously calm southern port of Odessa led to a fire that police said left at least 38 people dead.
At least two others were killed in the Black Sea port city during clashes outside the building.
The first serious offensive by the government in Kyiv and the dozens of deaths in Odessa sharply escalated the crisis that has led to the worst tensions between Russia and the West since the Cold War. The Kremlin said the battle for the separatist-held city of Slovyansk effectively destroyed the Geneva pact aimed at cooling the unrest in the deeply divided country.
An eyewitness on the ground in Odessa, who asked to remain anonymous for his security, told Al Jazeera that pro-Russians sought refuge in the building after clashes with youth from the pro-Ukraine camp, who had reportedly congregated in town for a sporting event.
Molotov cocktails, paving stones and explosive devices were thrown during the clashes.
“Now, what is striking is the total absence of law enforcement and crowd control,” the source said. “There is total incompetence.”
In a news release, the Russian Ministry of Foreign Affairs condemned the attacks, saying Russia is “outraged” and it condemns the violence “in the strongest possible terms,” while calling on Ukraine and the West to end the violence.
“Moscow sees the tragic events of May 2nd in Odessa in which allegedly 38 people died and 50 were injured as yet another manifestation of criminal irresponsibility by the Kyiv authorities, who allow insolent radical nationalists” to lead a “campaign of physical terror against supporters of federalization and real constitutional reforms in Ukraine,” the statement read.
“The tragic events in Odessa served as another confirmation of criminal use of force and intimidation, something that has nothing in common with the February 17 agreement and the Geneva Pact from April 17,” the statement continues.
The violence is some of the worst Odessa has seen since Ukrainian President Viktor Yanukovych was ousted in February over both his decision not to sign a pact with the European Union and broader concerns about corruption in his government.
The opposing sides have clashed in Odessa before, but the violence Friday is the first time fighting has turned deadly. Some residents said they feared both sides may try to seek retribution, possibly leading to more deaths.
Dmytro Spivak, a local parliamentarian, also told Ukrainian television that at least six young supporters of the government in Kyiv had been killed.
“It is abundantly clear that the pro-Russian side was very well armed, well organized and that this action was planned long ago,” he said, adding that police did little to stop the clashes.
Al Jazeera was not immediately able to verify Spivak’s claims.
After Ukrainian forces launched their offensive against pro-Russian militiamen in the eastern city of Slovyansk, at least seven deaths were reported.
Russian President Vladimir Putin's spokesman said the offensive "effectively destroyed the last hope for the implementation of the Geneva agreements," deals intended to defuse the crisis that has gripped Ukraine for months.
Also on Friday, U.S. President Barack Obama, in a briefing at the White House together with German Chancellor Angela Merkel, said that if Moscow did not use its alleged influence to stop attacks by pro-Russian militia in Ukraine before elections on May 25, it would impose further sanctions on Russia.
Al Jazeera and wire services