Violence flared in eastern Ukraine Sunday as Ukraine’s interior minister announced forces were attempting to regain control of official buildings in the city of Slovyansk from pro-Russian militant separatists, NBC News reported. One Ukrainian state security officer was killed and five wounded on the government side in what Ukraine’s interior minister Arsen Avakov called Sunday's "anti-terrorist" operation. Residents were warned to stay indoors and military helicopters were seen hovering above besieged buildings. The Russian news agency RIA reported that one pro-Moscow activist was killed in Slovyansk in clashes with forces loyal to the Kiev government.