UN Secretary-General Ban Ki-moon said Saturday that he was “deeply dismayed” over the execution of 47 people, including a prominent Shia cleric, in Saudi Arabia.

“Sheikh al-Nimr and a number of the other prisoners executed had been convicted following trials that raised serious concerns over the nature of the charges and the fairness of the process,” Ban said in a statement issued by his spokesperson’s office.

“[Ban] also calls for calm and restraint in reaction to the execution of Sheikh Nimr and urges all regional leaders to work to avoid the exacerbation of sectarian tensions,” the statement read.

Saudi Arabia’s Ministry of Interior announced Saturday the execution of 47 people on terrorism charges, according to the Saudi Press Agency.

Among those executed was Nimr Baqir al-Nimr, a Shia Muslim cleric who led mass protests against Saudi authorities in eastern Qatif province before his arrest in July 2012. He was later convicted of inciting sedition and revolt in a judgment approved by the Supreme Judiciary on Oct. 25.

Ban had raised the case of Nimr with Saudi authorities on a number of occasions, the UN statement said, urging Riyadh to commute all death sentences imposed in the country.

Following Nimr’s death, Shia Iran warned that Sunni-dominated Saudi Arabia would “pay a heavy price” for the killing. Also on Saturday, a group of Iranian protesters stormed the Saudi embassy in Tehran, setting fire to the building, according to the Iranian Students News Agency (ISNA).

“[Ban] deplores the violence by demonstrators against the Saudi Embassy in Tehran,” the UN said.

The two countries are fierce regional rivals and are currently involved in backing opposing sides in civil wars in Syria and Yemen. (Anadolu Agency)

•Photo shows UN Secretary-General Ban Ki-moon.