Iran's Supreme Leader Ayatollah Ali Khamenei had harsh words for Saudi Arabia on Sunday, issuing threats to Iran's regional rival following the execution of Shiite cleric Nimr al-Nimr on Saturday, along with 46 other people, on charges of terrorism.

"The unjustly spilled blood of this martyr will have consequences," Khamenei said, according to state news agency ISNA, warning Riyadh of "divine revenge."

Saudi Arabia, meanwhile, said Tehran was supporting terrorism through its condemnation of the execution.

Al-Nimr had called for increased rights for the Shiite Muslim population in the Sunni-majority country, although Khamenei insists he never advocated violence.

Anger across the region

The Supreme Leader's words came shortly after mass riots across the country in response to the execution. In Tehran, demonstrators broke into the Saudi embassy, torching the building and trashing its interior. Crowds also set fire to the Saudi consulate in the Iranian city of Mashhad.

The Iranian Foreign Ministry urged calm, while 40 demonstrators were arrested near the embassy.

In Iraq, Shiite leader Grand Ayatollah Ali al-Sistani also condemned the killing. "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."

Criticism from the West

The US, a key ally of Saudi Arabia, and the EU also expressed disapproval of the decision to execute al-Nimr. The execution "risks exacerbating sectarian tensions at a time when they urgently need to be reduced," the US State Department said.

EU foreign policy head Federica Mogherini issued a similar statement. The UN High Commissioner for Human Rights, meanwhile, said it wasn't clear if those executed had even received a fair trial.

The criticism comes as the US and the EU have sought to make inroads with Iran following a heralded nuclear deal earlier this year.

blc/se (AP, dpa)