A horrific fire last week that killed dozens in a hulking Odessa building where pro-Russian protesters had taken cover was likely sparked by rebels on the roof who accidentally dropped Molotov cocktails, according to a preliminary investigation by the government.
The finding is likely to further anger separatists in eastern Ukraine who view the new government in Kiev with deep suspicion. It comes as authorities said the situation on the border with Russia has grown increasingly tense, and France warned of the prospect of "chaos and civil war" if the presidential election set for this month is upended.
The two-month-old government has been pressing a military offensive in the east to try to quell a pro-Russian insurgency, but is increasingly losing its grip in the regions of Luhansk and Donetsk, which border Russia. The unrest spread Friday to the Black Sea port of Odessa, which was hit by rioting that led to a fire that claimed 42 lives.
Serhiy Chebotar, Ukraine's deputy interior minister, who is now working in Odessa, said Tuesday that the fire began on the top floors and quickly spread through the trade-union building, where pro-Russian protesters had taken refuge from a mob of pro-Kiev militants.
"The fire began from the roof. There were extremists there, we found casings and firearms," Mr. Chebotar said. "But something unexpected happened; their Molotov cocktails fell, and ignited the higher floors of the building."
This version of events is likely to be contested by grieving relatives of those who perished in the fire or died jumping out of windows. Four others were killed in the rioting that day.
Pro-Russian activists in Odessa believe the fire was a deliberate atrocity committed by Ukrainian nationalists. Russian media have compared the fire to the worst Nazi crimes against civiliansin World War IIand suggested it was a plot by Kiev.
"We are dealing with real genocide, a genocide of Russian and Ukrainian people in today's 21st century," the speaker of the lower house of Russia's parliament, Sergei Naryshkin, said of the fire, which he blamed on "riotous radicals," the Interfax news agency reported.
Acting President Oleksandr Turchynov on Tuesday dismissed the head of the Odessa regional administration, having already fired the chief of the regional police and much of his senior staff.
The fire occurred after a pro-Ukraine rally was attacked by pro-Russian protesters, whose ranks included a small group of armed militants. The fighting escalated before some people escaped to the building. Both sides threw Molotov cocktails.
Video footage shows some pro-Ukraine activists helping people trapped in the burning building escape by leaning scaffolding against the walls. There were other pro-Ukraine protesters who were attacking people.
Among the dead was Vadim Papura, a 17-year-old political-science student, whose funeral was Tuesday. He had taken part in the clashes and sought cover in the trade-union building, then jumped from the third floor to escape the flames, according to his friend Timur Lyubinski.
Mr. Papura's body was so disfigured that friends and family identified him by the striped pants he was wearing that day. His open coffin, with his face reconstructed, sat in front of the apartment block where he had once lived, as his parents, friends and fellow students gathered for the emotional service.