riyadh saudi king salman receive former lebanese prime minister saad al-hariri riyadh monday follow resignation saudi media report hariri announce resignation saturday riyadh say believe assassination plot accuse iran saudi arabia arch-rival lebanese ally hezbollah sow strife arab world king salman meet resign lebanese prime minister saad al-hariri short ago presenter saudi-owned al-arabiya television say hariri resignation topple coalition government include shi ite muslim group hezbollah thrust lebanon back frontline saudi-iranian regional rivalry risk open-ended political crisis state news agency spa carry picture hariri king salman greet sit together palatial set hariri surprise resignation televise speech air al-arabiya tv draw criticism meet controversy beirut even question whether hariri resignation voluntary lebanese justice minister salim jreissati say monday lebanon president would take step regard hariri resignation hariri return abroad stress resignation must voluntary president michel aoun say early monday political leaders responsive call calm strengthen security national unity hariri shock resignation saudi king receive ex-lebanon pm hariri riyadh