The moves follow the ransacking of Saudi diplomatic missions in the Islamic Republic, violence that was sparked by the Saudis' execution of a prominent Shiite cleric.

The island kingdom of Bahrain announced it would sever its ties completely from Iran, as Saudi Arabia did late on Sunday.

Within hours, the United Arab Emirates (UAE) announced it would downgrade its own diplomatic ties to Tehran, bringing them down to the level of the charge d'affaires and would from now on focus entirely on the business relationships between the two countries.

The Saudi decision to halt diplomatic relations came after the mass execution of Sheikh Nimr al-Nimr and 46 others - the largest carried out by Saudi Arabia in three-and-a-half decades - laid bare the sectarian divisions gripping the region.

Shiite protesters took to the streets from Bahrain to Pakistan while Arab allies of Sunni-ruled Saudi Arabia quickly lined up behind the kingdom.

Al-Nimr was a central figure in the Arab Spring-inspired protests by Saudi Arabia's Shiite minority until his arrest in 2012. He was convicted of terrorism charges but denied advocating violence.

Bahrain enjoys particularly close relations with Saudi Arabia, which like Bahrain's leadership is suspicious of alleged Iranian efforts to destabilise the island nation, which has a tiny Shiite-majority but is Sunni-ruled.

Riyadh, along with the UAE, sent tanks and troops to Bahrain in 2011 to quell widespread anti-government protests spearheaded by Bahrain's Shiite majority.

Bahraini officials have blamed Iran for training militants and attempting to smuggle arms into the country, which hosts the US Navy's 5th Fleet.

In October, Bahrain ordered the acting Iranian charge d'affaires to leave within 72 hours and recalled its own ambassador from Tehran after alleging Iran sponsored "subversion" and "terrorism" and funnelled arms to militants.

The UAE, a country of seven emirates, has a long trading history with Iran and is home to many ethnic Iranians.

Saudi foreign minister Adel al-Jubeir announced the cut in Riyadh-Tehran relations late on Sunday and gave Iranian diplomatic personnel 48 hours to leave his country. All Saudi diplomatic personnel in Iran have been called home.

The move could affect the annual hajj pilgrimage. Mohammad Ali Esfanani, spokesman of the Judicial and Legal Committee of the Iranian parliament, said security issues and the fact that Iranian pilgrims would not have consular protection inside the kingdom made halting the pilgrimage likely, according to the semi-official ISNA news agency.

Both Saudi Arabia and Iran are yet to make any formal announcement about how the diplomatic spat would affect the hajj, a pilgrimage to Islamic holy sites in Saudi Arabia required of all able-bodied Muslims once in their life. The hajj this year likely will begin in early September, though Muslims travel to the holy sites all year long as well.

"When a country has cut diplomatic relations with us, it means it is hostile with us," Mr Esfanani said. "It appears that protection (of pilgrims) and security issues will prevent hajj from taking place."

When Saudi Arabia severed ties with Iran from 1988 to 1991, Iran stopped its pilgrims from attending the hajj. Also, with Saudi diplomatic missions closed in Iran, it will make it difficult for Iranians to get visas for the hajj.

World powers have sought to calm the tensions, with a Russian state news agency quoting an unnamed senior diplomat as saying Moscow is ready to act as a mediator in the escalating conflict. The RIA Novosti news agency did not say whether Moscow had made the mediation proposal to either side.

In Washington, State Department spokesman John Kirby said the Obama administration believes "diplomatic engagement and direct conversations remain essential in working through differences".

"We will continue to urge leaders across the region to take affirmative steps to calm tensions," Mr Kirby said.

Sudan is also severing its diplomatic relations with Iran. It says the decision takes immediate effect.

The Sudanese foreign ministry made the announcement in a statement carried by Sudan's state news agency.