BEIRUT (Reuters) - Lebanon s president stressed that stability is  a red line  after the prime minister s shock resignation, Justice Minister Salim Jreissati said on Monday after meeting the president. Saudi King Salman received Lebanese Prime Minister Saad al-Hariri in Riyadh on Monday, two days after he quit, Saudi-owned al-Arabiya television reported, without elaborating. In a televised speech, Hariri had said he feared an assassination plot against him and accused Iran along with its Lebanese ally Hezbollah of sowing strife in the Arab world.  His resignation stunned Beirut s political establishment, brought down the coalition government and sparked a new political crisis. It has thrust Lebanon into the front line of the regional rivalry between Sunni Muslim Saudi Arabia and Shi ite Muslim Iran that has also buffeted Syria, Iraq, Yemen and Bahrain.  Lebanese President Michel Aoun convened a meeting with ministers and top security officials at the Baabda palace on Monday to assess the security situation. Aoun told them political leaders had been responsive to calls for calm, strengthening security and national unity, his office said.  The president will take no steps regarding the prime minister s resignation before Hariri returns from abroad, the justice minister said at a press conference after the meeting. Aoun said security, economic, financial, and political stability is  a red line , Jreissati said.   The president is waiting for Hariri s return to hear from him personally. This indicates a sovereign vision...and that the resignation must be voluntary in every sense.   Aoun was also set to meet the finance minister and central bank governor later on Monday. 