Police in the Ukrainian port city of Odessa say at least 38 people have died in a building fire that broke out during fighting between pro-Russian separatists and supporters of the central government in Kyiv.
A police statement said the fire broke out in a trade union building, but offered few other details. The Russian news agency RIA Novosti said 50 others were injured, including 10 police officers. Odessa, a key Black Sea port, had largely escaped the pro-Russian separatist-driven violence gripping large parts of eastern Ukraine.
The Odessa violence comes just hours after Ukrainian government forces launched the first major assault on the rebel-held eastern city of Slovyansk.
Late Friday, Western media said Ukrainian forces had seized rebel checkpoints on the outskirts of the city, but had not advanced toward its heavily fortified center. Separatists shot down two Ukrainian helicopters during the fighting, killing two crew members. A third occupant was reported captured.
Ukraine's Acting President Oleksandr Turchynov said rebels had suffered heavy losses, including many killed and wounded. But he offered no details.
In Moscow, a spokesman for Russian President Vladimir Putin called the Ukrainian offensive "a criminal act." He also said it had "effectively destroyed the last hope" for implementing an April 17 international accord aimed at defusing the crisis. Mr. Putin on Thursday demanded Ukraine withdraw all military personnel from the troubled region near the Russian border.
In Washington, President Barack Obama -- speaking alongside German Chancellor Angela Merkel -- said that if Russia's leadership continues to destabilize eastern Ukraine, the U.S. and European Union will move quickly to impose additional penalties -- including both diplomatic and economic sanctions.
In New York, Western powers and Russia used an emergency session of the United Nations Security Council to accuse each other of failing to take appropriate steps to de-escalate the crisis. British Ambassador Mark Lyall Grant said "the scale of Russian hypocrisy is breathtaking."
For his part, Russian Ambassador Vitaly Churkin accused the West of applying double standards in the crisis by condoning the current Ukrainian offensive, after urging then-Ukrainian president Viktor Yanukovych not to deploy troops when his government in Kyiv was under siege earlier this year.
Pro-Russian gunmen control a number of key buildings in the key eastern Ukrainian industrial city of Donetsk and have declared a May 11 referendum on whether to secede from Ukraine and join Russia.
A similar vote last month led to Russia's annexation of the Crimean peninsula.