The bitter rivalry may be more bad news for the long-suffering people of Syria. Also, Iran's President Hassan Rouhani has come off looking ineffectual.
The kingdom's execution of Sheikh Nimr al-Nimr, who was highly critical of the Saudi government, marks a turning point in Saudi-Iranian relations and has sent shock waves through the region.
The Saudi-Iran rivalry has been a fundamental fault line in the Middle East for decades and complicates most every major issue in the region, from the Syrian civil war to global oil markets.
A cold war in the Middle East just turned a lot hotter. Saudi Arabia, a Sunni power, and Iran, a Shiite one, have long been bitter rivals, but always maintained diplomatic relations — until now.
Saudi Arabia's execution of Shiite cleric Sheik Nimr al-Nimr has inflamed sectarian conflict and been strongly condemned by Iran. Now the Saudis have ordered Iranian diplomats out of the country.
Angry over the execution of Shiite cleric Sheik Nimr al-Nimr in Saudi Arabia, protesters gathered at the Saudi Embassy in Tehran, reports Iran's semi-official news agency. Some entered the building.
Secretary of State John Kerry said the move was "one of the most significant steps" in fulfilling the July nuclear agreement between Iran and six world powers.