BEIRUT — Bahrain and Sudan joined Saudi Arabia in severing diplomatic relations with Iran on Monday as the worst crisis in three decades between the region’s rival Sunni and Shiite powers drew worldwide expressions of alarm.

The United Arab Emirates, meanwhile, recalled its ambassador from Tehran in a downgrading of ties to focus mainly on commercial affairs. Dubai is the base for many Iranian-run businesses.

As the diplomatic storm widened, so did the efforts at international damage control.

Russia offered to mediate, the United Nations dispatched a senior envoy for crisis talks in Riyadh and Tehran, and a growing list of nations expressed concern at the implications of the rupture – touched off by Saudi Arabia’s execution of a prominent Shiite cleric as part of its largest mass execution of prisoners in more than 35 years.

Iran said Saudi Arabia made a “strategic mistake” that could only further divide the region and fuel militancy during crucial battles against the Islamic State and efforts to end Syria’s civil war.

In further signs of spillover: sectarian violence flared in Iraq, police clashed with protesters in Bahrain, and financial markets dropped sharply.

The Persian Gulf nation of Bahrain – a close Saudi ally and home to the U.S. Navy’s 5th Fleet – ordered Iranian diplomats to leave within 48 hours. Sudan said it also was severing diplomatic ties with Iran, which had sought to improve relations with Sudan in recent years to make it an economic and military foothold in Africa.

The moves could boost pressure on other Saudi allies around the region to take diplomatic action against Iran. Already, security forces around the region were on higher alert.

In Bahrain, police fired tear gas Monday at mainly Shiite protesters denouncing Saudi Arabia’s execution of the cleric, Nimr Baqr al-Nimr, on Saturday, news agencies reported. In 2011, Saudi Arabia sent troops into the island nation to back the Sunni rulers seeking to crush a Shiite-led uprising demanding a greater voice in the country’s affairs.

Global financial markets were roiled by the deepening tensions between the OPEC giants. U.S. stocks opened sharply lower Monday, and Asian markets plunged on a mix of worries over the Middle East impasse and weak Chinese manufacturing data. Oil prices seesawed amid the uncertainty.

Underscoring the worries, the United Nations pulled its chief envoy for Syria, Staffan de Mistura, away from that conflict for a round of talks with Saudi and Iranian officials. De Mistura is expected in Riyadh on Monday and will travel to Tehran later in the week, said U.N. deputy spokesman Farhan Haq.

In Washington, White House press secretary Josh Earnest urged Iran and Saudi Arabia “to show restraint and not further inflame tensions that are on quite vivid display in the region.” He told reporters that “all sides” could do more to bridge sectarian divides.

Asked if the rift could harm efforts to reach a political solution in Syria, Earnest said, “We’re hopeful that it won’t.” He said a reason for optimism was that “it is so clearly in the interest of both countries to advance a political solution” in Syria.

Earnest said Secretary of State John F. Kerry has been in contact with his counterparts in the region but that President Obama has not made calls to fellow leaders in recent days.

In explaining its decision to expel Iranian diplomats, Saudi Arabia cited “hostile” comments by Iran after the execution of Nimr on Saturday, as well as the subsequent attack on its embassy in Tehran.

Saudi Foreign Minister Adel al-Jubair told reporters in Riyadh late Sunday that the diplomats were given 48 hours to leave the country. But Saudi diplomats had already departed Iran after angry crowds ransacked and burned the Saudi Embassy in Tehran overnight Saturday, in retaliation for the execution of Nimr.

As part of the diplomatic freeze, Saudi Arabia halted air traffic between the two countries, the Saudi civil aviation agency said. It was unclear how the decision could affect special flights for Iranian pilgrims seeking to visit Islam’s holiest sites, but Jubair told the Reuters news agency that Iranians were still welcome for the annual hajj and other pilgrimages.