On International Workers' Day, pro-Russian protesters marched through central Donetsk in eastern Ukraine calling for a referendum on the region's future. They laid siege to the prosecutor's office, surrounding a group of beleaguered riot police. Fighting broke out – the cops hurled out teargas, the protesters chucked stones. Before long the police, who were outnumbered, were forced to surrender. The Kiev government's hold on the east of Ukraine is looking weaker by the day.