KYIV—Kyiv police detained a man who forced his way into Ukraine’s main government building on Wednesday morning and threatened to detonate a grenade, head of the National Police Ihor Klymenko said. “We were able to get out of this situation, neutralize this criminal,” Klymenko told a briefing. He said the man, whose demands were unclear, was identified as a veteran of the war with Russia-backed separatist in eastern Ukraine. Klymenko said the man had a real grenade and he had given himself up after talking to a friend and fellow veteran. Video on the incident online, which could not immediately be verified by Reuters, showed a man in jeans and a striped T-shirt in one of the lobbies of the building where government ministers meet. He is holding something in his right hand and is shouting that he has a grenade. The prime minister’s office is in the building, but …