Clashes broke out between government forces and pro-Russian separatists in eastern Ukraine on Thursday with the interior ministry in Kyiv saying its forces had killed "up to five" militants. According to a ministry statement, during an "anti-terrorist operation" its forces removed three checkpoints manned by armed groups at entrances to the eastern town of Slovyansk. "During the armed clash up to five terrorists were eliminated," the statement said. Earlier on Thursday, Ukrainian Interior Minister Arsen Avakov wrote on Facebook that police cleared the city hall in Mariupol and that it "has been freed to resume work." Separatist forces confirmed the loss of the city hall. Clashes were also reported by the defense ministry in the eastern town of Artemivsk, 40 km (25 miles) southeast of Slovyansk, where authorities repelled an attack on an army base. The defense ministry said in a statement that nearly 100 separatists "opened fire with automatic weapons, machine guns and used grenades" in the attack on the military base. Ukrainian government forces on Tuesday re-launched a military operation to oust pro-Russian protesters and masked gunmen who have been occupying government buildings across eastern Ukraine for nearly two weeks.