washington u.s. president donald trump south korean act president hwang kyo-ahn agree take step strengthen joint defense capabilities defend north korea nuclear threat white house say sunday telephone call two leaders president trump reiterate ironclad commitment defend south korea include provision extend deterrence use full range military capabilities white house say statement also say trump hwang discuss upcoming visit new u.s. defense secretary japan south korea share concern north korea top agenda unite state south korea agree deploy terminal high altitude area defense thaad system design protect north korea grow nuclear ballistic capabilities despite objections china say radar could penetrate chinese territory north korean leader kim jong un say jan. country close test-launching intercontinental ballistic missile icbm state media say launch could come time north korea maintain nuclear missile program violation repeat round international sanction trump south korea 's hwang agree strengthen defenses north korea white house