IRAN’S top leader has warned Saudi Arabia it faces “divine revenge” over the execution of an opposition Shiite cleric while Riyadh accused Tehran of supporting terrorism, escalating a war of words hours after protesters stormed the Saudi Embassy in Tehran.

Saudi Arabia announced the execution of Sheikh Nimr al-Nimr on Saturday along with 46 others, including three other Shiite dissidents and a number of al-Qaida militants. Al-Nimr was a central figure in protests by Saudi Arabia’s Shiite minority until his arrest in 2012, and his execution drew condemnation from Shiites across the region.

Iran’s Supreme Leader Ayatollah Ali Khamenei condemned the execution Sunday in a statement on his website, saying al-Nimr “neither invited people to take up arms nor hatched covert plots. The only thing he did was public criticism.”

Iran’s powerful Revolutionary Guard said Saudi Arabia’s “medieval act of savagery” in executing the cleric would lead to the “downfall” of the country’s monarchy.

Saudi Arabia’s Foreign Ministry said that by condemning the execution, Iran had “revealed its true face represented in support for terrorism.”

The statement, carried by the official Saudi Press Agency, accused Tehran of “blind sectarianism” and said that “by its defense of terrorist acts” Iran is a “partner in their crimes in the entire region.”

Iraq’s top Shiite authority Grand Ayatollah Ali al-Sistani sided with Iran, describing the execution as an “aggression”.

“We received with deep sadness and regret the news of the martyrdom of a group of our brothers in the region,” he said.

“The spilling of their pure blood — including of the late cleric Sheikh Nimr al-Nimr, may his soul rest in peace — is an injustice and an aggression,” Sistani said.

Al-Nimr was convicted of terrorism charges but denied ever advocating violence.

The executions have plunged the Middle East into further turmoil. Sunni Saudi Arabia and Shiite Iran are locked in a bitter rivalry, and support opposite sides in the wars in Syria and Yemen. Iran accuses Saudi Arabia of supporting “terrorism” in part because it backs Syrian rebel groups, while Riyadh points to Iran’s support for the Lebanese Hezbollah and other Shiite militant groups in the region.

The Iranian Foreign Ministry has summoned the Saudi envoy in Tehran to protest, while the Saudi Foreign Ministry later said it had summoned Iran’s envoy to the kingdom to protest Iran’s criticism of the execution, saying it represented “blatant interference” in its internal affairs.

PROTESTS STRIKE SAUDI EMBASSY

Angry crowds earlier protested over Saudi Arabia’s execution of a top Shiite cleric by hurling petrol bombs and stormed the kingdom’s embassy in Tehran, ISNA news agency reported.

The embassy demonstrators were cleared out by police and 40 arrests have been made, Tehran’s prosecutor said, adding that more detentions could follow.

“The fire has destroyed the interior of the embassy,” an eyewitness said.

The violent rally was in response to the death of 56-year-old Nimr al-Nimr, who had been a key figure in anti-government protests in the kingdom’s oil-rich east. The execution infuriated Shiite-majority Iran and Iraq.

Posts on Twitter appeared to show crowds breaking into the Saudi embassy and setting fires.

ISNA reports that the country’s top police official, General Hossein Sajedinia, rushed to the scene and police were working to disperse the crowd.

SPIRALLING TENSIONS

The influential cleric was among 47 Shiite and Sunni prisoners executed on Saturday and his death threatened to further damage Sunni-Shiite relations in a regional struggle playing out across the Middle East between the kingdom and its regional foe Iran.

Video shows protesters inside Saudi embassy in Tehran pic.twitter.com/DEmsNLI6ZG — Sobhan Hassanvand (@Hassanvand) January 2, 2016

Shiite leaders across the region swiftly condemned Riyadh and warned of sectarian backlash as Saudi Arabia insisted the executions were part of a justified war on terrorism. Also executed Saturday were al-Qaeda detainees who were convicted on launching a spate of attacks against foreigners and security forces a decade ago.

Angry of execution of Sheikh #NimrAlNimr Iranian burned down #Saudi Embassy in Tehran pic.twitter.com/vM6TPieKym — M.Reza Noroozpour (@noroozpour) January 2, 2016

The execution now becomes another focal point for sectarian and political wrangling between Saudi Arabia and Iran. The two regional rivals back opposing sides in civil wars in Yemen and in Syria. Saudi Arabia was also a vocal critic of the recent Iranian agreement with world powers that ends international economic sanctions in exchange for limits on the Iranian nuclear program.

Iranian politicians warned that the Saudi monarchy would pay a heavy price for the death of Sheikh Nimr al-Nimr. The Iranian Foreign Ministry summoned the Saudi envoy in Tehran to protest, and parliament speaker Ali Larijani said the execution would prompt “a maelstrom” in Saudi Arabia.

Al-Nimr’s execution could also antagonise the Shiite-led government in Iraq, which has close relations with Tehran. The Saudi embassy in Baghdad, which had been closed for nearly 25 years, was reopened on Friday. An influential Shiite militia in Iraq, known as Asaib Ahl Al-Haq, called on the government Saturday to close down the embassy.

WORLD LEADERS SPEAK OUT

Iraqi Prime Minister Haidar al-Aabadi Tweeted Saturday night that he was “shocked and saddened” by al-Nimr’s execution, adding that, “peaceful opposition is a fundamental right. Repression does not last.”

Bloody handprints on the gates of the #KSA embassy gate in #Tehran pretty symbolic for the new relationship status pic.twitter.com/sKdvS6qTvT — Tonton du Bled (@NextDoorArab) January 3, 2016

A spokesman for United Nations Secretary-General Ban Ki-moon has issued a statement conveying he was “deeply dismayed” over the executions in Saudi Arabia. He also called for calm and restraint.

In a statement on Saturday, US State Department spokesman John Kirby called on Saudi Arabia to ensure fair judicial proceedings and permit peaceful expression of dissent while working with all community leaders to defuse tensions after the executions.

Kirby said the US is particularly concerned that the execution of a prominent Shiite cleric and political activist risks making sectarian tensions worse at a time when they urgently need to be reduced.

Hundreds of al-Nimr’s supporters protested in his hometown of al-Qatif in eastern Saudi Arabia, in neighbouring Bahrain where police fired tear gas and bird shot, and as far away as northern India.

Germany’s Foreign Ministry said the cleric’s execution “strengthens our existing concerns about the growing tensions and the deepening rifts in the region.”

His death comes 11 months after Saudi Arabia issued a sweeping counter-terrorism law after Arab Spring protests shook the region in 2011 and toppled several longtime autocrats. The law codified that the kingdom could prosecute as a terrorist anyone who demands reform, exposes corruption or otherwise engages in dissent or violence against the government.

The convictions of those executed Saturday were issued by Saudi Arabia’s Specialized Criminal Court, established in 2008 to try terrorism cases.

To counter Arab Spring rumblings that threatened to spill into eastern Saudi Arabia, the kingdom sent troops in 2011 to crush Shiite protests demanding more political powers from the Sunni-led, fraternal monarchy of Bahrain. More security forces were also deployed that year to contain protests in Saudi Arabia’s oil-rich east, where al-Nimr rallied youth who felt disenfranchised and persecuted.

A Saudi lawyer in the eastern region said that three other Shiite political detainees were also executed from among the 47. The lawyer spoke on condition of anonymity for fear of reprisal.

Advocacy organisation Reprieve, which works against the death penalty worldwide, said two of the Shiites executed were teenagers when they were arrested. Reprieve said Ali al-Ribh was 18-years-old and Mohammed al-Shuyokh was 19 at the time of arrest in 2012. Both were convicted on charges related to anti-government protests held in eastern Saudi Arabia.

Saudi Arabia says all those executed were convicted of acts of terrorism. Al-Nimr and the three others mentioned had been charged in connection with violence that led to the deaths of several protesters and police officers.

Saudi Arabia’s top cleric Grand Mufti Sheikh Abdulaziz Al Sheikh defended the executions as in line with Islamic Sharia law. He described the executions as a “mercy to the prisoners” because it would save them from committing more evil acts and prevent chaos.

CRITICS OF THE DEATH PENALTY

Islamic scholars around the world hold vastly different views on the application of the death penalty in Sharia law. Saudi Arabia’s judiciary adheres to one of the strictest interpretations, a Sunni Muslim ideology referred to as Wahhabiism.

Because Saudi Arabia carries out most executions through beheading and sometimes in public, it has been compared to al-Qaeda the extremist Islamic State group, which also carry out public beheadings and claim to be implementing Sharia.

Saudi Arabia strongly rejects the comparisons and points out that it has a judicial appeals process with executions ultimately aimed at combating crime.

In Lebanon, senior Shiite cleric Abdul-Amir Kabalan described al-Nimr’s execution as “a grave mistake that could have been avoided with a royal amnesty.”

The Lebanese Shiite militant group Hezbollah issued a statement calling al-Nimr’s execution an “assassination” and a “ugly crime.” The group added that those who carry the “moral and direct responsibility for this crime are the United States and its allies who give direct protection to the Saudi regimen.”

In a press conference Saturday, Saudi Interior Ministry spokesman Maj. Gen. Mansour al-Turki said the executions were carried out inside prisons and not in public, as is sometimes the case. The Interior Ministry, which announced the names of all 47 people executed in a statement, said a royal court order was issued to implement the sentences after all appeals had been exhausted.

The Saudi television airwaves were flooded with pro-government analysts saying the executions are a blow to critics who accuse the kingdom of not doing enough to counter extremism. One analyst pointed out that France declared a state of emergency and prioritised security after the recent Paris attacks that killed more than 120 people.

Meanwhile, the execution of al-Qaeda militants raised concerns over revenge attacks. The extremist group’s branch in Yemen, known as al-Qaeda in the Arabian Peninsula, had threatened violence against Saudi security forces last month if they carried out executions of its fighters.

One of the executed was Faris al-Shuwail, a leading ideologue in al-Qaeda’s Saudi branch who was arrested in August 2004 during a massive crackdown on the group following the series of deadly attacks.

The executions took place in the capital, Riyadh, and 12 other cities and towns. Of those executed, 45 were Saudi citizens, one was from Chad and another was from Egypt.

In announcing the verdicts, Saudi state television showed mugshots of those executed. Al-Nimr was No. 46, expressionless with a grey beard, his head covered with the red-and-white scarf traditionally worn by men in the Arab Gulf region.

Al-Nimr, who was in his 50s, never denied the political charges against him, but maintained he never carried weapons or called for violence.

At his trial, he was asked if he disapproved of the Al Saud ruling family because of speeches in which he spoke out forcefully against former Interior Minister and late Crown Prince Nayef bin Abdelaziz, who is King Salman’s elder brother.

“If injustice stops against Shiites in the east, then (at that point) I can have a different opinion,” the cleric responded, according to his brother Mohammed al-Nimr, who attended court sessions and spoke to The Associated Press just days before the Oct. 2014 verdict.

US-based Human Rights Watch’s Middle East director Sarah Leah said “regardless of the crimes allegedly committed, executing prisoners in mass only further stains Saudi Arabia’s troubling human rights record.” She said al-Nimr was convicted in an “unfair” trial and that his execution “is only adding to the existing sectarian discord and unrest.”

Al-Nimr’s brother told the AP by telephone that the executions came as a “big shock” because “we thought the authorities could adopt a political approach to settle matters without bloodshed.” He urged people to “adopt peaceful means when expressing their anger.”

Mohammed’s son Ali, the cleric’s nephew, is also facing execution, but his name was not among those listed Saturday. He was 17 years old in February 2012 when he was arrested. He was later convicted, and his death sentenced upheld, on charges of attacking security forces and taking part in protests, among other charges

Saudi Arabia carried out at least 157 executions in 2015, with beheadings reaching their highest level in the kingdom in two decades, according to human rights groups.