Demonstrations erupted across the Middle East Sunday as Shiite Muslims protested Saudi Arabia’s execution of prominent Shiite cleric Nimr al-Nimr. Protesters in the Iranian capital, Tehran, broke into the Saudi embassy early Sunday morning — setting fires and throwing papers from the roof before being dispersed by police. Demonstrations also took place in Bahrain, Turkey, Pakistan and northern India.

By Sunday afternoon crowds of protesters had gathered outside Saudi embassies in Beirut and Tehran, and protests were expected in al-Nimr’s hometown of al-Qatif in eastern Saudi Arabia.

Al-Nimr’s execution adds a rancorous new chapter to the ongoing Sunni-Shiite struggle that continues to play out across the Middle East with Iran and Saudi Arabia as the primary antagonists. Here’s a look at the aftermath and the regional implications.

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WHO WAS SHEIKH NIMR AL-NIMR?

Al-Nimr, who was in his 50s, was a widely revered Shiite Muslim cleric from eastern Saudi Arabia who was convicted in Oct. 2014 of sedition and other charges and sentenced to death. He was an outspoken government critic and a key leader of Shiite protests in eastern Saudi Arabia in 2011. He was also a critic of the government of Bahrain, where a Sunni-led monarchy suppressed protests by Shiites who make up the majority of the tiny island nation. Saudi Arabia sent troops to help Bahrain crush the uprising, concerned it would spread and destabilize other Arab Gulf countries.

Al-Nimr, however, also spoke out against the Iranian-backed government in Syria for killing protesters there.

He directly criticized the Al Saud ruling family for its domestic policies and forcefully spoke out against individual royal family members. Al-Nimr did not deny the political charges against him, but maintained he never carried weapons or called for violence.

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WHY IS HIS EXECUTION IMPORTANT?

His death is seen by some as a warning to anyone thinking of calling for reforms and wider political freedoms in Saudi Arabia. His death also strikes a sensitive chord for Saudi Shiites who claim they are discriminated against by authorities in the kingdom, where many ultraconservatives Sunnis view Shiites as heretics.

Several Shiites mosques and places of worship were targeted by Sunni extremists in 2015 in eastern Saudi Arabia, despite attempts by security forces to clamp down on Islamic State group supporters who have also targeted police.

Al-Nimr’s execution came as a surprise to even his own family, his brother Mohammed al-Nimr told The Associated Press. Despite harsh verdicts against government critics, activists are typically given long jail sentences even after initial appeals that uphold death sentences.

His death is expected to further exacerbate the proxy wars for regional supremacy being fought across the region by Saudi Arabia and Iran. The two rival nations currently back opposing sides in civil wars in both Syria and Yemen.

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HOW WILL THIS IMPACT SUNNI-SHIITE RELATIONS?

Iran’s Shiite clerics have used al-Nimr’s death to lash out at Saudi Arabia, which is founded upon an ultraconservative Sunni ideology known as Wahhabism. Many extremist Wahhabis regard all Shiites as heretics.

Supreme Leader Ayatollah Ali Khamenei warned Riyadh of “divine revenge” and both Saudi and Iran summoned each other’s diplomatic envoys in protest.

Iran and Saudi have been vying for leadership in the Muslim world since Iran’s 1979 revolution, which elevated to power hard-line Shiite clerics. The U.S. war in Iraq further enflamed religious and ethnic tensions by leading to a Shiite-led government in Baghdad and a crucial shift in the sectarian balance of power in the region.

After Arab Spring protests erupted in 2011, Saudi Arabia and Iran entered into a fierce proxy war in Syria, where they are supporting opposite sides of the conflict, and in Yemen, where Saudi Arabia has been bombing Iranian-allied rebels since March. They also support opposing political groups in Lebanon, Iraq and Bahrain.

(AP)