Saudi Arabia's Sunni allies rallied behind the kingdom on Monday and several joined Riyadh in severing or downgrading diplomatic relations with Tehran, in the wake of a row over the execution of a Shia cleric.
Bahrain and Sudan cut all ties with Iran, and the United Arab Emirates (UAE), home to hundreds of thousands of Iranians, downgraded its relations. Saudi Arabia broke off relations on Sunday after a mob stormed its embassy in Tehran, amid outrage that a leading Shia cleric was among 47 people executed by the Sunni Muslim kingdom on Saturday.
On Monday Saudi Foreign Minister Adel al-Jubeir announced that flights between the two countries would be stopped, ending commercial relations and barring its citizens from travel to the Islamic Republic.
Iran is the world's main Shia Muslim power while Saudi Arabia is a leading Sunni Muslim country, and they back opposing sides in the Syrian and Yemeni conflicts.
Iran has accused Saudi Arabia of using the attack on the embassy as an "excuse" to sever ties and further increase sectarian tensions, after Shia Muslims across the world denounced Saudi Arabia's killing of Shia cleric Nimr al Nimr.
Saudi Arabia executed Nimr and three other Shia Muslims on terrorism charges on Saturday, alongside dozens of Sunni jihadists. Iran hailed Nimr as a "martyr" and warned Saudi Arabia's ruling Al Saud family of "divine revenge".
Saudi Foreign Minister Adel al-Jubeir said Iran was creating "terrorist cells" among the kingdom's Shia minority.
A man was shot dead in Saudi Arabia's Eastern Province late on Sunday, and two Sunni mosques in Iraq's Shia-majority Hilla province were bombed in the fallout from the dispute between the Middle East's top Sunni and Shia powers.
Shia groups united in condemnation of Saudi Arabia while Sunni powers rallied behind the kingdom, hardening a sectarian split that has torn apart communities across the Middle East and nourished the jihadist ideology of Islamic State.
Demonstrations to protest Nimr's execution are planned on Monday in Baghdad and southern Shia cities, following a call by influential anti-American cleric Moqtada al Sadr.
An early gathering of demonstrators in Baghdad tried to pass through barbed wire into the fortified Green Zone where the Saudi embassy is located but police repelled them, a Reuters cameraman said.
Iran's Foreign Minstry said on Monday that Saudis were "increasing clashes and tension" in the Middle East region. "Saudi Arabia sees not only its interests but also its existence in pursuing crises and confrontations and attempts to resolve its internal problems by exporting them to the outside," said spokesman Hossein Jaber Ansari.
France and Germany on Monday echoed a call by the US for Saudi Arabia and Iran to talk to each other and reduce tensions, while China said it was concerned about the prospect of conflict in the Middle East intensifying as a result of the row.
The European Union's foreign policy chief warned Iran's foreign minister on Sunday that renewed tension between Iran and Saudi Arabia could wreck efforts to find a political solution for the crisis in Syria.
Russia, meanwhile, offered itself up as a mediator, Russian news agencies reported.
"As friends we would be ready to play, if it is demanded, an intermediary role in ... settling the existing contradictions and any new ones that arise between these two countries," RIA cited an anonymous Foreign Ministry source as saying.
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