More than 2,000 pro-Russian militants on Sunday stormed the police headquarters in the Ukrainian port city of Odessa, where 42 people died in clashes two days ago.
In a bid to calm the marauding mob, police released dozens of pro-Russians who had been arrested on Friday during running battles with supporters of the pro-Western government in Kiev.
Local officials said the mob forced the release of 67 of the more than 150 detained since Friday. Shouts of acclaim greeted them when they emerged.
An AFP reporter on the scene said the crowd shouted "fascists, fascists" as they attacked the building.
Some youths used a van as a battering ram to smash through a metal door while others threw rocks through windows and attacked police vehicles.
The protesters, some armed with batons and other improvised hand-held weapons, then poured through into an interior courtyard.
A young police officer quelled the crowd by announcing they would release the prisoners, and soon afterwards the first man emerged, raised his fist in triumph and ran into the welcoming embrace of his comrades.
The rest followed quickly through a guard of honour created by the crowd who cried "freedom, freedom" as they passed.
The mob then vacated the interior courtyard but around 2,000 remained in the streets, watched closely by riot police.
Odessa, a scenic Black Sea port that is home to more than one million people, was still in shock after running battles on Friday between pro-Russians and pro-Kiev protesters culminated in an inferno that left 38 dead.
Most of those trapped inside a trade union building in central Odessa were thought to have been pro-Russian supporters who had barricaded themselves in.
The two sides were lobbing petrol bombs at each other when the blaze erupted, sparking frantic efforts to escape.
According to local health officials, 30 died when they were overcome by fumes and eight in the desperate bid to escape.
A further four died from gunshot wounds during the initial clashes, officials said.
Ukraine's prime minister, Arseniy Yatsenyuk, who visited Odessa earlier Sunday, blamed the deaths on what he called "inefficient" police.
Both sets of protesters have voiced outrage that firefighters took so long to respond to the blaze.