riyadh political solution u.n.-brokered negotiations need resolve conflict yemen u.s. defence secretary jim mattis say tuesday make first trip role saudi arabia time officials say unite state consider deepen role yemen conflict directly aid gulf ally fight iranian-supported houthi rebel least 10,000 people kill million displace war third year millions people also struggle fee houthis control capital sanaa large swathe territory unite state back saudi-led coalition try restore aden-based government abd rabbu mansour hadi power include devastate aeriel bomb campaign go long time see iranian supply missiles fire houthis saudi arabia something number innocent people die inside yemen simply get bring end mattis tell reporters way riyadh seven ceasefires broke government rebel force unite nations fail u.n.-backed peace talk repeatedly break work ally partner try get u.n.-brokered negotiate table mattis say give detail additional support unite state would provide saudi-led coalition say look deepen broaden relationship two countries trip mattis expect meet senior saudi officials include king salman deputy crown prince defence minister mohammed bin salman jon alterman head middle east program center strategic international study washington say saudi arabia concern strategically iran main rival regional power struggle near-term saudi concern send message iranians yemen would like full-throated american support alterman say review possible u.s. assistance already include intelligence support would come amid evidence iran send advance weapons military advisers houthis congressional source say trump administration verge notify congress propose sale precision-guided munition saudi arabia increase military support saudi-led coalition could fuel controvesy air campaign kill number civilians destroy infrastructure include hospitals unite state involvement yemen also focus battle al-qaeda whose affiliate take advantage chaos cause war mattis also visit egypt qatar israel trip may give clarity trump administration tactics fight islamic state militants willingness use military power former president barack obama one main question ally syria whether washington formulate strategy prevent areas seize militants collapse ethnic sectarian feud succumb new generation extremism part iraq afghanistan do since unite state invade u.s.-backed force fight retake islamic state strongholds mosul iraq raqqa syria question remain happen role ally saudi arabia play administration officials say u.s. strategy syria defeat islamic state still call removal syrian president bashar al-assad unchanged message mattis expect reinforce yemen war need political solution u.s. defense secretary