Protesters stormed and torched the Saudi Arabian Embassy in Tehran on Saturday after the execution of a prominent Shiite cleric ignited sectarian tensions across the already inflamed region, jeopardizing US diplomacy aimed at tamping down conflicts in the Middle East.
The unrest erupted after Saudi authorities announced that Sheik Nimr Baqr al-Nimr, 56, was among 47 people put to death.
Some were killed by firing squad, others by beheading, according to a statement from Saudi Arabia's Interior Ministry. Most were Sunnis accused of participating in al-Qaida attacks in the kingdom.
Nimr, however, was one of four Shiites put to death for political activism and the leading figure in the anti-government demonstrations that swept the mostly Shiite east of the country in 2011, inspired by the Arab Spring protests elsewhere in the region.
The death sentence was carried out despite international appeals for clemency and repeated warnings from the kingdom's archenemy in the region, Iran, that there would be consequences if the popular cleric were killed.
The US State Department, which had refrained from publicly joining the appeals for Nimr's life, said it had raised concerns at the highest levels of the Saudi government about the judicial process. In a statement, it called on Saudi Arabia "to respect and protect human rights" and to permit "peaceful expression of dissent."
"We are particularly concerned that the execution of prominent Shia cleric and political activist Nimr al-Nimr risks exacerbating sectarian tensions at a time when they urgently need to be reduced," the State Department said in a statement. "In this context, we reiterate the need for leaders throughout the region to redouble efforts aimed at de-escalating regional tensions."
Shiites around the world expressed outrage, potentially complicating a surge of US diplomacy aimed at bringing peace to the troubled region, according to Toby Matthiesen, an expert on Saudi Arabia at the University of Oxford.
"Nimr had become a household name amongst Shiite Muslims around the world. Many had thought his execution would be a red line and would further inflame sectarian tensions," he said. "So this will complicate a whole range of issues, from the Syrian crisis to Yemen."
Saudi Arabia and Iran are backing rival sides in Syria's war, and their enmity risks derailing a diplomatic effort led by the United States and Russia to convene peace talks between the factions in Geneva this month.
The two feuding powers also support opposing sides in the war in Yemen and more broadly find themselves in opposition in the deeply divided politics of the mixed Sunni-Shiite nations of Iraq and Lebanon.
The Obama administration's hopes that the conclusion last summer of an agreement limiting Iran's nuclear program would help bridge the sectarian divide between Tehran and the United States' biggest Arab ally were further diminished by the eruption of fury that followed Nimr's death.
Angry demonstrations were held in several Iranian cities, including Tehran, where protesters broke into the Saudi Embassy, ransacked it and set it ablaze. Video posted on Twitter showed crowds smashing windows with crowbars and overturning furniture. Demonstrators also torched the Iranian consulate in the city of Mashhad.
The Iranian Foreign Ministry warned that there would be repercussions.
"The Saudi government will pay a heavy price for adopting such policies," said Foreign Ministry spokesman Hossein Jaber Ansari, calling the execution "the depth of imprudence and irresponsibility" on the part of the Saudi government, according to Iranian news agencies.
Iran summoned the Saudi charge d'affaires in Tehran to complain about the execution, and Saudi Arabia reciprocated by calling in the Iranian ambassador in Riyadh to protest the "hostile" remarks made by Iranian officials.
The execution also triggered renewed unrest in both Saudi Arabia and neighboring Bahrain, after years of calm following the suppression of the demonstrations in 2011.
Activists from both countries used Twitter and other social media accounts to appeal for a new uprising. In the eastern Saudi city of Qatif, hundreds of people took to the streets, and Saudi officials expanded patrols and bolstered checkpoints to deter further upheaval, according to a Qatif activist who spoke on the condition of anonymity because he feared for his safety.
The Nimr family issued a statement expressing shock and dismay at the execution, and urging "restraint and self-control" among Nimr's followers.
The cleric's brother, Mohammed al-Nimr, pledged on his Twitter account that the democracy movement would endure.
"Wrong, misled and mistaken [are] those who think that the killing will keep us from our rightful demands," he tweeted after the execution was announced.
In Bahrain, where demonstrations by the country's Shiite majority against the ruling Sunni royal family were quelled by the intervention of Saudi troops in 2011, there were reports of scattered protests in several Shiite towns and villages. Videos posted on YouTube by Bahraini activists showed hundreds of people, some wearing T-shirts featuring the bearded cleric's face, marching through the streets in at least four locations.
Nimr had long served as the voice of Saudi Arabia's Shiite minority, the target of discrimination, but he rocketed to prominence in 2011, articulating the sentiments not only of Shiites but also of many others in the region demanding change after decades of authoritarian rule.
He had consistently advocated nonviolence, and his views transcended the Sunni-Shiite divide, said Maryam al-Khawaja, a Bahraini human rights activist with the Gulf Center for Human Rights who lives in exile in Denmark.
"He said Sunnis and Shiites should unite and that anyone who supports the oppressors should be condemned," she said, citing a 2012 speech Nimr delivered in which he condemned Syrian President Bashar al-Assad, who is from the Shiite-affiliated Alawite sect and is backed by Iran, and the region's Sunni authoritarian leaders, including the Saudi royal family.
"This was a big part of why he became problematic for the Saudi regime, because he refused to abide by the sectarian discourse that is basically enforced on everyone," Khawaja said.
Nimr was arrested by Saudi security forces in 2012, after being shot in the legs during a car chase. He had been charged with "instigating unrest and undermining the kingdom's security," as well as delivering speeches against the government and defending political prisoners.
Condemnations also poured in from other Shiite figures and organizations. Lebanon's Hezbollah movement said it held the United States and its allies responsible for Nimr's execution because "they are giving direct protection to the Saudi regime."
"This crime will remain a black mark that will plague the Saudi regime, which has been committing massacres since its inception," Hezbollah said in a statement.
In Iraq, there was an outpouring of anger from Shiite leaders and politicians, with the influential cleric Moqtada al-Sadr calling on Shiites in Iraq and across the region to protest the execution. He told Iraqis to take their demonstrations to the newly reopened Saudi Embassy in Baghdad's fortified Green Zone, which welcomed a new Saudi ambassador to Iraq on Friday for the first time in nearly 25 years.
Iraq's al-Sumaria television channel reported that Shiites in Karbala were demanding that Prime Minister Haider al-Abadi close the Saudi Embassy.
Abadi condemned the execution but offered no immediate response. Yemen's Houthi rebel movement also issued a condemnation on its website.
The advocacy group Amnesty International criticized all of the executions, including those of the accused al-Qaida operatives, saying those killed had not been given fair trials. Nimr's execution, in particular, suggested that Saudi authorities "are using the death penalty, in the name of counter terror, to settle scores and crush dissidents," Amnesty International said in a statement.
Saudi Arabia carried out at least 157 executions in the past year, a record number according to human rights groups. Nimr's nephew, Ali Mohammed al-Nimr, is on death row - he was sentenced last year to death by crucifixion for participating in the protests while he was 16 or 17 years old, also drawing widespread international condemnation.