Iran's supreme leader said today that Saudi Arabia will face 'divine revenge' for executing a top Shiite cleric whose death sparked protests in which the kingdom's embassy in Tehran was firebombed.

Ayatollah Ali Khamenei's remarks underlined the fury felt in Iran and other regional countries over the killing yesterday of Nimr al-Nimr, who spent more than a decade studying theology in the Islamic republic.

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 Shiite activists and Sunnis who the Saudi interior ministry said had been involved in Al-Qaeda killings.

Some were beheaded, and were shot by firing squad, said the ministry.

While Shiite leaders hit out at the executions, the United Arab Emirates and Bahrain defended their Sunni ally, saying they were necessary to confront extremism.

Saudi Arabia in turn accused Iran of sponsoring terror and undermining regional stability.

Khamenei called the killing of Nimr "a political mistake by the Saudi government" which would "haunt its politicians". His comments came ahead of protests planned to start in Tehran at 3:00 pm (1730 IST).

"The unjustly spilt blood of this martyr will have quick consequences," Khamenei told clerics in the Iranian capital. "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," he said of Nimr.

The executions prompted protests in at least one city in Saudi Arabia's oil-rich Eastern Province, where Shiites complain of marginalisation, as well as in Iraq and Bahrain.

In Tehran, the Saudi embassy was ransacked after protesters threw petrol bombs and stormed the building. The kingdom's consulate in Mashhad, Iran's second biggest city, was also set on fire.

Saudi foreign ministry spokesman Mansur al-Turki called Iran's reaction "irresponsible", and summoned Tehran's envoy in protest.

The embassy demonstrators were cleared out by police and 40 arrests have been made, Tehran's prosecutor told the ISNA news agency, adding that more detentions could follow.

"The fire has destroyed the interior of the embassy," an eyewitness told AFP.

Websites had carried pictures of protesters clutching the Saudi flag, which had been pulled down and members of the crowd were able to climb onto the roof of the embassy before they were made to leave.