PARIS/WARSAW—France assured Poland on Wednesday of European Union support in its stand-off with Belarus, but reminded Warsaw it needed to resolve a row with the bloc over its values and the rule of law. Polish Prime Minister Mateusz Morawiecki met French President Emmanuel Macron as part of a diplomatic effort to rally support for a tough response to what European Commission chief Ursula von der Leyen called an attempt by Belarus to use migrants to destabilize the EU. While reaffirming his solidarity with Poland, Macron reiterated concerns over the rule of law and “called on the Polish government to find a solution that safeguards the core values of the European Union”, his office said. With thousands of people fleeing the Middle East and other hotspots stranded on the EU’s eastern border, Poland, Lithuania, and Latvia are on the front line of what the EU says is a crisis engineered by …