The alleged assassination plot linking Iranian operatives with a plan to target Saudi's Arabia's Washington ambassador has sharply raised tensions between the two countries.

The Saudi government called the plot a “despicable violation of international norms, standards and conventions.” Saudi Arabia and Iran have long been geopolitical rivals, but the 2011 Arab Spring protests sparked a dramatic rise in tension.

The Saudi kingdom is considered the traditional leader of the Arab Gulf states and Sunni Muslims worldwide. It is the custodian of Islam's holiest sites. Iran is a Shi'ite-dominated Islamic republic populated by ethnic Persians.

In March, the Saudis sent tanks and troops into the Sunni-ruled island kingdom of Bahrain to crush a protest led by the country's Shi'ite majority. The crackdown soured relations between Tehran and the Gulf Arab monarchies, whose Shi'ite activists are regularly accused of links with their co-religionists in Iran.

For decades, the two sides vied for regional influence through proxy politicians and covertly funded militias.

Iran dominates in Syria, and with the militant Arab groups Hezbollah in Lebanon and Hamas in the Palestinian territories.

The Saudis are allied with the Gulf monarchies, regional powerhouse Egypt and the other main Palestinian faction, Fatah.

Iran has long pursued a nuclear program it insists is for non-military use, but which Saudi Arabia and the United States believe is aimed at producing atomic weapons. Saudi leaders have suggested that if Iran were to develop a nuclear bomb, it may feel obligated to do the same. Riyadh recently negotiated a $60 billion-arms deal with the United States.

The 1979 Iranian revolution sent ripples across the region, threatening Saudi Arabia and its allies. The Arab Gulf monarchies host large numbers of disgruntled Shi'ite minorities and fear their potential mobilization by Tehran.

In 1981, the Saudis co-founded the Gulf Cooperation Council in order to solidify Iran's containment.