Iranian state television reported Saturday that the diplomats had been summoned in protest over Nimr's execution.

Ayatollah Ahmad Khatami, a cleric in largely Shia rival Iran, said repercussions against the Sunni Saudi rulers would "wipe them from the pages of history."

Meanwhile, the Hezbollah group referred to Nimr's execution as an "assassination."

"Hezbollah categorically condemns the heinous crime committed by the Saudi regime represented in the assassination of the eminent scholar and jihadist Sheikh Nimr Baqir al-Nimr on flimsy pretexts and corrupt Sunni group that regard Shiites as heretics and has often targeted them in its attacks."

Iran, Saudi Arabia’s regional rival were critical of the clerics execution, calling it politically and religiously motivated.

"Instead of focussing on Islamic State terrorists and threatening the region and the whole world, the Saudis execute a prominent figure like al-Nimr," Jaber Ansari, Iran’s foreign ministry spokesperson said, referring to the radical Sunni militia in Syria and Iraq.

Meanwhile, German foreign ministry official, who declined to be named, expressed concern on Saturday about the execution, reaffirming the country’s standpoint that the dealth penalty is an inhumane form of punishment.

"The execution of Nimr al-Nimr strengthens our existing concerns about increasing tensions and deepening rifts in the region," said the official.

Berlin's human rights envoy, Christoph Straesser, was also critical.

Nimr's execution by Saudi authorities will lead to the overthrow of the kingdom’s Sunni rulers, Iraq’s former Prime Minister Nuri al-Maliki predicted.

"We vehemently condemn these repugnant sectarian practices and confirm that the execution of Sheikh al-Nimr will oust the Saudi regime," Maliki said in a press statement.

Students demonstrate against execution

Meanwhile, well-known Iraqi Shiite cleric Moqtada al-Sadr called for rallies in Gulf countries and Iraq to protest the sheikh's execution.

"I ask that the Shiites of Saudi Arabia…show courage in responding even through peaceful demonstration, and the same Shiites in the Gulf, so as to deter injustice and government terrorism in the future," he said on his website.

"I urge…angry demonstrations in front of Saudi sites and interests, and I urge the government to refrain from opening the Saudi embassy," he said.

Riyadh this week opened its embassy in Iraq, which had been closed in 1990 after the Iraqi invasion of Kuwait.

In the Iranian holy city of Qom, seminary students protested against Saudi Arabia's execution of Nimr, the Mehr news agency reported.

A photograph published by Mehr showed dozens of men, some of them in the robes and turbans of the Shiite Muslim clergy, marching through the city holding up pictures of the dissident Saudi cleric.

Nimr was executed along with three other Shiites and dozens of alleged members of the al Qaeda terrorist organization on Saturday.

jlw/rc (Reuters, dpa)