Ukraine's PM has blamed the country's security services for failing to stop violence in the southern city of Odessa that left more than 40 people dead.
Arseniy Yatsenyuk told the BBC there would be "full, comprehensive and independent investigation".
Most of the victims were pro-Russian separatists who died in a fire after barricading themselves in a building.
The PM's comments came as Ukrainian troops surrounded the pro-Russian stronghold of Sloviansk in the east.
Mr Yatsenyuk said of the Odessa violence: "I personally blame the security service and law enforcement office for doing nothing to stop this crackdown."
Mr Yatsenyuk said: "These security forces are inefficient and they violated the law."
He said the police chief of the Odessa region had been removed and that the prosecutor's office had started an investigation.
"The prosecutor's office is to investigate everyone – starting with the chief of police, his deputies and every single police officer."
Some 42 people died in Odessa on Friday, most of them in the fire at the Trade Unions House, where separatist protesters had barricaded themselves following running battles with pro-Kiev activists.
Mr Yatsenyuk blamed pro-Russian groups for "provoking the unrest".
He accused Russia and pro-Russian protesters of orchestrating "real war… to eliminate Ukraine and eliminate Ukrainian independence".
Asked about pro-Russian groups who have taken over many buildings in towns in the east, Mr Yatsenyuk said: "We haven't entirely lost the control… much will depend on the local population, whether they support peace and security."
Ukrainian troops have encircled Sloviansk as the government seeks to wrest control from the separatists.
The BBC's Sarah Rainsford, in the regional capital Donetsk, says that while it appears the Ukrainian forces have sealed off the roads in and out of the town, they are moving around it and concentrating on smaller towns nearby.
Our correspondent spoke to a resident of Sloviansk who said people there were expecting it to be stormed.
Gunfire was reported overnight in Kostyantynivka, where one separatist checkpoint was dismantled, and Mariupol as Ukrainian forces tried to reclaim government offices.
There had been heavy fighting in the town of Kramatorsk on Saturday, with the interior ministry saying the army had retaken a television tower.
Kiev officials said at least two people were killed in the town, although Russian state television reported 10 deaths.
Ukraine's National Security and Defence Council chief Andriy Parubiy said on Sunday that the military would expand the "active stage of the operation in towns where extremists and terrorists are carrying out illegal activities".
Ukraine's President Viktor Yanukovych was overthrown by pro-Western protesters in February.
Russia then annexed the Crimean peninsula – part of Ukraine but with a Russian-speaking majority – in a move that provoked international outrage.