U.S. President Barack Obama meets with Turkish President Recep Tayyip Erdogan (L) at the U.S. ambassador's residence during the World Climate Change Conference 2015 (COP21) in Paris, France December 1, 2015. Obama urged Turkey on Tuesday to reduce tensions with Moscow after the downing of a Russian warplane and to seal its border with Syria to choke off the supply of money and fighters to Islamic State militants. REUTERS/Kevin Lamarque