Syria's political opposition in exile urged all Arab countries on Monday to sever diplomatic ties with Iran after Saudi Arabia, a strong supporter of the Syrian opposition, cut relations with Tehran.The Syrian National Coalition declared its support for Riyadh's move, calling on "all Arab and Islamic countries to take a similar step" and criticised what it said was Iran's support for militias in Syria and Iraq.Iran supports Syrian Bashar al-Assad, whose forces, backed also by Russia, are fighting against an array of groups including rebels backed by Saudi Arabia and other countries in the region.Sunni-Shi'ite tension in the region spilled over on Saturday night when Iranian protesters stormed the kingdom's embassy in Tehran after Saudi Arabia executed a prominent Shi'ite cleric.