The execution in Saudi Arabia of a prominent Shiite cleric Saturday sparked outrage in neighbouring Iraq, from protesters threatening the royal family to politicians calling for diplomatic action.

Hundreds of people demonstrated in the holy Shiite city of Karbala and some leaders urged the government to close down the newly reopened Saudi embassy in Baghdad.

Nimr al-Nimr, a driving force of protests that broke out in 2011 in the Sunni-ruled kingdom's east, was among 47 people executed in Saudi Arabia.

The office of Hadi al-Mudaressi, an Iraqi cleric whose brother has a strong following among Bahraini Shiites notably, organised a protest near the mausoleum of Imam Hussein in Karbala.

"No red lines from now on", "We will reap your souls, Saud and Khalifah", read some of the banners, referring to the Saudi and Bahraini ruling families.

"This is what I tell Al-Saud from the sacred land of Hussein: I swear to God that the sheikh's blood was not spilled in vain," said Said Saad al-Mussawi, one of the protesters.

"We will make the earth shake under your feet," he said.

Sheikh Ibrahim al-Ashtari, from Mudaressi's office, said he wanted "the Iraqi government to take a clear and honest position regarding this major tragedy."

A cleric from Bahrain who was at the protest, Sheikh Habib al-Jamri, said the world should react to Nimr's execution.

"Sheikh Nimr was an icon for Islamic resistance," he told AFP.

"His words were his weapon. They couldn't defeat his words so they detained him, tortured him and today executed him in front the world's eyes, like a challenge to global conscience."

Prime Minister Haider al-Abadi expressed "great shock" and warned of the destabilising potential of Nimr's execution.

"Freedom of speech and peaceful opposition are basic human rights granted by divine and international laws. Violating them impacts the region's security, stability and social fabric," he said in a statement.

Several Sunni clerics also condemned Nimr's execution, which looked likely to strain a recent attempt at diplomatic rapprochement between the two countries.

- Diplomatic tension -

Khalaf Abdelsamad, who heads the parliamentary bloc of Iraq's Shiite Dawa party -- to which both Abadi and his predecessor Nuri al-Maliki belong -- also said Baghdad should take action.

"Abdelsamad urges the Iraqi government to close down the Saudi embassy, expel the ambassador and execute all Saudi terrorists in Iraqi prisons," a statement from his office said.

The embassy only just reopened on December 15, a quarter of a century after relations were broken over Iraq's invasion of Kuwait. The ambassador himself has only been in the country three days.

A justice ministry spokesman said 61 Saudis were detained in Iraqi prisons six months ago. He could not immediately provide a recent figure.

"The execution of Sheikh al-Nimr will have serious consequences and bring about the end of the Al-Saud (royal family's) rule," Abdelsamad's office said.

Asaib Ahl al-Haq, one of the most powerful Shiite militias in the country, reacted with similar demands.

Abu Mahdi al-Mohandis, a top leader in the powerful Hashed al-Shaabi (Popular Mobilisation) paramilitary group that is dominated by Tehran-backed militias, condemned Nimr's execution.

"Even as the rulers of Saudi Arabia are supporting terror in the entire world by sending takfiris, weapons and car bombs to Muslim countries, today they executed the most honest man in Saudi Arabia," he said in a statement.

Takfir is a part of the ideology of some extremist Sunni groups -- such as the Islamic State group that controls parts of Iraq and Syria -- that considers other Muslims infidels.

Mohandis has close ties with Tehran, which reacted by warning Saudi Arabia that it would pay a "high price".

"The Saudi government supports terrorist movements and extremists, but confronts domestic critics with oppression and execution," an Iranian foreign ministry spokesman said.

Saudi Arabia executed more than 150 people in 2015.

Top Iraq cleric says Saudi executions an 'aggression'
Najaf, Iraq (AFP) Jan 3, 2016 - Iraq's political and religious leaders united Sunday in condemnation of the execution by Saudi Arabia of a prominent Shiite cleric which they saw as a deliberate sectarian aggression.

"We received with deep sadness and regret the news of the martyrdom of a group of our brothers in the region," Iraq's top Shiite authority Grand Ayatollah Ali al-Sistani 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.

Other leading Shiite clerics in Iraq have reacted with outrage to the execution on Saturday by the Saudi authorities of Nimr and other Shiite activists.

They were among a total of 47 people, most of them described by the interior ministry as involved in killings by Al-Qaeda.

Moqtada al-Sadr, a well-known cleric who heads the Saraya al-Salam militia, said Nimr's execution was a "horrible attack" against Shiites and called for international condemnation.

Mohammed Taqi al-Mudaresi, another cleric who is based in the holy Shiite city of Karbala, took a harder line.

"The execution of the martyr (Nimr) isn't just a declaration of war against the People of the House (Shiites) but against all Muslims," he said in a statement.

The Iraqi foreign ministry accused Saudi Arabia of using the fight against terrorism to silence its opposition.

"The terrorism charges he (Nimr) was executed for should have been brought against the terrorist criminals of Daesh (Islamic State group), not an opponent expressing the will of the nation," a statement said.

- Small protests -

Echoing comments made by Iraqi Prime Minister Haider al-Abadi on Saturday, the foreign ministry said Riyadh was threatening its own and the region's stability.

"Executing a religious man and peaceful opponent, while turning a blind eye on the clerics issuing dozens of takfiri fatwas and supporting terrorists with weapons and money is blatant sectarian discrimination," the statement said.

"It will not serve the stability of the region."

Takfir is a part of the ideology of some extremist Sunni groups -- such as the Islamic State group that controls parts of Iraq and Syria -- that considers other Muslims infidels.

Several small protests took place in Baghdad and elsewhere in Iraq, including in the southern town of Nasiriyah.

On Palestine street in the capital, a few dozens protesters, including several clerics, chanted slogans against Riyadh and carried portraits of Nimr.

"The House of Saud has opened the gates of hell on its own regime," said one cleric, Ahmed al-Shahmani.

The executions also sparked a wave of anger in neighbouring Iran, where protesters firebombed the Saudi embassy in Tehran, and in Bahrain where Shiite protesters clashed with police.

Several clerics and protesters in Iraq have also called for the closure of the Saudi embassy and said that the envoy should be expelled over Nimr's execution.

The embassy reopened on December 15, a quarter of a century after diplomatic ties were severed over the invasion of Kuwait.

It is located in the fortified part of central Baghdad known as the "Green Zone", which is home ot most ley institutions and embassies.

Ambassador Thamer al-Sabhan, who arrived in Iraq four days ago, posted a message on social media in which he said they are being "looked after by the Iraqi government".