moscow russian president vladimir putin u.s. president discuss civil war syria tuesday putin stress importance find political solution conflict meet syria president trump putin speak telephone hour cover topics include syria ukraine iran north korea afghanistan white house official say early conversation come putin host syrian president bashar al-assad three hours talk monday preparation push moscow end syria conflict islamic state drive self-styled caliphate iraq syria accord kremlin putin tell trump syrian leader confirm adherence political process run constitutional reform president parliament elections message send necessity keep sovereignty independence territorial integrity syria reach political settlement base principals work full-scale negotiation process syria kremlin say wednesday turkish president tayyip erdogan iranian president hassan rouhani whose countries back oppose side syria conflict travel russia meet putin aim advance syrian peace process putin stress importance trump call coordinate efforts special service countries two leaders also discuss north korea stress expediency find ways solution diplomatic mean putin inform trump outcome meet syria 's assad