Ukraine has seen its deadliest violence in months after the conflict between nationalist and pro-Russian militias spread to the southern port city of Odessa. At least 46 people died on Friday when a massive blaze erupted at a base where the two sides were fighting. On Sunday, pro-Russian separatists attacked an Odessa police station, freeing dozens of prisoners. The Ukrainian government has vowed to intensify its campaign against the separatists, with large parts of Ukraine now appearing on the brink of war. In a move that could help defuse tensions among foreign powers, seven observers with the Organization for Security and Cooperation in Europe were freed on Saturday after over a week in captivity by pro-Russian forces.