TEHRAN (Dispatches) – Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei and Iraq's top Shia cleric Grand Ayatollah Ali al-Sistani on Sunday condemned Saudi Arabia's execution of Sheikh Nimr al-Nimr, warning ahead of protests that the killing was an injustice that could have serious consequences.
The remarks highlighted the fury over the execution of Nimr, who spent over a decade studying theology in the Islamic Republic.
Ayatollah Khamenei said Saudi rulers would face "divine revenge" for their actions, which prompted massive protests in Iran on Saturday and Sunday.
Top officials in Iraq, Lebanon and Syria condemned the execution of Nimr, a force behind anti-government protests in Saudi Arabia in 2011 in the east of the country.
The 56-year-old cleric was put to death along with 46 Shia activists and Sunnis who the Saudi interior ministry said were involved in Al-Qaeda killings. Some were beheaded, others were shot by firing squad.
Ayatollah Khamenei called the execution of Sheikh Nimr "a political mistake by the Saudi government" that would "haunt its politicians".
"The unjustly spilt blood of this martyr will have quick consequences," Ayatollah Khamenei said in a speech to clerics.
"God will not forgive. This scholar neither encouraged people into armed action nor secretly conspired for plots but the only thing he did was utter public criticism rising from his religious zeal."
Ayatollah Sistani's remarks were not as strong as Ayatollah Khamenei's but in a statement he alluded to repercussions from the executions.
"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," he said.
In Lebanon, Hezbollah chief Seyyed Hassan Nasrallah said the Saudi regime is looking at "the abyss”.
"When a regime loses its mind, that means it has reached the abyss,” he said.
"The signs of the end of this corrupt criminal unjust Takfiri terrorist regime have begun to emerge,” he noted, saying, "The killing of our brothers, the spilling of our blood will not go just like that and they must be afraid, they must hide.”
On Sunday, Nimr's brother, Muhammad, said he had been told the corpse would not be returned to the family.
The executions prompted protests Saturday in at least one city in Eastern Province, where Shias complain of marginalization, as well as in Iraq and Bahrain.
The incidents came after the United States and European Union expressed alarm at the executions, with Washington warning Riyadh risked "exacerbating sectarian tensions at a time when they urgently need to be reduced".
UN Secretary General Ban Ki-moon said he was "deeply dismayed" by the state-sanctioned killings.
Ayatollah Khamenei, however, denounced the anemic reaction and slammed the silence of those who claim to be advocates of freedom, democracy and human rights, and their support for the Saudi regime which is killing innocent people just for criticizing them.
"The Muslim world and the whole world must feel responsibility toward this issue,” the Leader said.
Torturing the Bahraini people and destruction of their mosques and homes in addition to the bombardment of the Yemeni people for over 10 months were other instances of crimes committed by the Saudi regime, he added.
"Those who are honestly interested in the fate of humanity, and the fate of human rights and justice must follow up on such issues and should not remain indifferent to this situation,” Ayatollah Khamenei said.
In Iraq, hundreds demonstrated in the holy Shia city of Karbala, and Moqtada al-Sadr, a prominent Shia cleric, urged further protests Sunday.
Lebanon's Hezbollah movement said Saudi Arabia's rulers were "global criminals", and said Nimr's execution was a "heinous crime".
Iran's Islamic Revolution Guards Corps said Saudi Arabia's "medieval act of savagery" in executing the cleric would lead to the "downfall" of the country's monarchy.
Executions have soared in Saudi Arabia since King Salman ascended the throne a year ago -- 153 people put to death in 2015, nearly twice as many as in 2014. Rights watchdogs have repeatedly raised concern about the fairness of trials in the kingdom.