MOSCOW—Russia is prepared for a split with the European Union if the EU imposes new crippling sanctions amid a dispute over the treatment of opposition leader Alexei Navalny, the nation’s top diplomat warned Friday. In response to a question about Moscow’s willingness to rupture links with the EU, Foreign Minister Sergey Lavrov said in televised remarks that Russia doesn’t want to be isolated but must increase its self-sufficiency to face potential EU sanctions. “We don’t want to be isolated from international life, but we must be ready for that,” Lavrov said. “If you want peace, you must prepare for war.” Asked if Russia is heading toward a split with the European Union, Lavrov replied, “We proceed from the assumption that we are ready for that.” He emphasized the importance of economic ties with the 27 EU nations, adding that Russia would continue engaging in mutually beneficial cooperation. At the same …