BERLIN—The European Union must be prepared to enact more sanctions against Russia if the situation in and around eastern Ukraine or on the Belarus-Poland border escalates, German Chancellor Angela Merkel said on Thursday. Speaking at a joint news conference in Berlin with her Polish counterpart Mateusz Morawiecki, the outgoing Chancellor said the EU had to be united on the issues of Belarus’s “weaponisation” of migrants against Poland and Russia’s deployment of troops to near its border with Ukraine. “Any further aggression against the sovereignty of Ukraine would carry a high price,” Merkel said, adding that defusing the situation should always be the preferred option. She later spoke by phone with Ukraine’s President Voldoymyr Zelenskiy. His office said the two had agreed on the need for a coordinated response to “threats” from Russia. Both Russia and Ukraine staged military drills this week following weeks of rising tensions between Kyiv and Moscow, …