Bahrain and Sudan, both close allies of Saudi Arabia, have joined the kingdom and cut diplomatic relations with Iran, while the United Arab Emirates, another Saudi ally, has downgraded them.

The steps come just days after Iranian protesters stormed the Saudi Embassy in Tehran in an apparent response to the kingdom’s execution over the weekend of a prominent Shiite cleric. Saudi Arabia severed diplomatic relations with Iran after the embassy protest, recalling its diplomats from the Islamic republic and giving Iranian diplomats 48 hours to leave the country.

In a statement, Bahrain said it was cutting relations with Iran “after the criminal cowardly attacks on the Embassy of the Kingdom of Saudi Arabia in Tehran and its consulate in the city of Mashhad.”

Sudan’s Foreign Ministry said Khartoum was cutting relations with Tehran in “response to the barbaric attacks on the Saudi Arabian embassy in Tehran and its consulate in Mashhad.” A statement from the Ministry of Foreign Affairs said the Emirates were downgrading ties with Tehran “in the light of Iran’s continuous interference in the internal affairs of Gulf and Arab states, which has reached unprecedented levels.”

Hossein Jaber Ansari, an Iranian Foreign Ministry spokesman, said the steps continued the Saudi “policy of increasing tension and clashes in the region.”

At issue is Saudi Arabia’s announcement on Saturday that it had executed 47 people on terrorism charges. Among them was Sheikh Nimr al-Nimr, who, as my colleague Marina Koren reported, was sentenced to death in October 2014 after being convicted of sedition and other charges. The Shiite cleric was a critic of the Saudi monarchy and had led protests in the eastern part of the country, where many Saudi Shiites live. The execution sparked protests by Shiites across the world, including in Iraq, Bahrain, Pakistan, and Iran, where protesters stormed the Saudi Embassy in Riyadh, as well as the consulate in Mashhad.

Although relations between Saudi Arabia, which is mostly Sunni, and Iran, which is predominantly Shiite, have never been warm, the tensions mark the worst deterioration in ties in recent years. It’s been some time coming: The two countries are on opposite sides of the civil war in Yemen, where the Saudis support the government and the Iranians the Houthi rebels; and in Syria, where Riyadh supports some rebel groups and Iran the government of President Bashar al-Assad. They have also parried in Bahrain, where a Sunni ruler governs a mostly Shiite population, and in Iraq, where Iran holds considerable influence over the predominantly Shiite government; and traded barbs over the death toll of the stampede at the Hajj last September.

The latest tensions have prompted fears of a region-wide sectarian conflict (indeed, on Monday, two Sunni mosques in Iraq were bombed and a cleric killed), but they also complicate U.S. efforts to forge a global coalition against the Islamic State group in the region. ISIS, as the Islamic State is also known, controls territory across Iraq and Syria, and Western nations see the group’s defeat as a pivotal step toward bringing about a semblance of stability to the Middle East. Worsening relations between the region’s two most powerful Muslim nations are likely to make that more difficult, though both countries ostensibly oppose ISIS.

Western nations, including the U.S., condemned Nimr’s execution, while Federica Mogherini, the EU’s foreign-policy chief, has urged both countries to resolve their differences. John Kirby, the U.S. State Department spokesman, said the U.S. believes “diplomatic engagement and direct conversations remain essential in working through differences.”