Saudi Arabia has severed diplomatic ties with Iran, as an escalating war of words between the two archrivals threatened to derail a renewed international bid to halt the conflict in Syria. [...] The United States is expected to repeat its appeal for restraint and calm when the State Department’s undersecretary for public diplomacy and public affairs, Richard Stengel, meets the Saudi undersecretary for international communication and media, Abdulmohsen Alyas, in Washington on Monday.