abu dhabi u.s. president donald trump defense secretary arrive unite arab emirates saturday talk one washington close ally middle east jim mattis debut trip region pentagon chief expect meet abu dhabi crown prince sheikh mohammed bin zayed al-nahayan u.s. embassy representatives u.s. officials disclose detail agenda late january trump crown prince speak telephone white house say discuss proposal safe zone syrian refugees displace conflict mattis retire marine general review u.s. war plan islamic state syria iraq familiar figure gulf arab rulers former leader central command oversee u.s. military operations region mattis say senate confirmation hear iran big destabilise force middle east policies contrary interest view play well gulf arabs hope trump administration check see surge iranian support paramilitary ally syria iraq yemen lebanon fellow shi ite muslims bahrain saudi arabia oil-producing eastern province unite arab emirates also key u.s. ally fight al qaeda yemen trump 's defense chief visit uae first middle east trip