KYIV—Ukraine’s foreign minister warned Russia on Thursday that an attack on his country would incur “political, economic, and human losses” and would be too costly. Russia has been building up forces near its border with Ukraine, and Kyiv, the United States, and NATO have voiced concerns about a possible Russian attack—a suggestion the Kremlin has dismissed as false. “We are not trying to guess what is in [Russian President Vladimir] Putin’s head,” Ukrainian Foreign Minister Dmytro Kuleba told a televised briefing. “We are working to give him a clear understanding—a new attack on Ukraine will be too costly, so it is better not to do it.” He said Kyiv’s main goal was to restrain Russia from “further aggressive actions.” “To do this, Moscow must clearly understand what political, economic, and human losses it will incur in the event of a new stage of aggression,” Kuleba said. The head of Ukraine’s …