The Iranian government will uphold the principles of international relations by making every effort to arrest and prosecute all those involved in the assault on the Saudi Embassy in Tehran.
This was stated by Iran's permanent envoy, Gholamali Khoshroo, in a letter to UN Secretary-General Ban Ki-moon on Monday, IRNA reported.
The embassy was stormed by protesters on Saturday night following the Saudi kingdom's execution of Shia Muslim cleric Sheikh Nimr al-Nimr, along with three other Shias and dozens of Sunni convicts.
Riyadh reacted the next day by a decision to cut relations with Tehran, in an escalation of already simmering tensions between the two regional powers, which back opposing sides in conflicts across the region.
"The Islamic Republic of Iran reaffirms its commitment to the relevant international law and treaties, particularly the 1963 convention governing consular relations and the 1961 convention governing diplomatic relations, and it will spare no effort to arrest and prosecute all those responsible," Khoshroo said.
The Iranian envoy noted that President Hassan Rouhani has instructed the relevant authorities, including the Interior Ministry, to vigorously investigate the matter alongside the judiciary.
Following the embassy storming, Rouhani issued a statement, criticizing the move as "absolutely unjustifiable" and noting that "the Interior Ministry is tasked with investigating the event resolutely in cooperation with the judiciary and the Intelligence Ministry to identify the attackers and bring them to justice".
Khoshroo promised in the letter that Tehran will take measures to ensure such incidents do not happen in future.
In the end, the envoy asked that the letter be circulated to all 193 UN member states.
***Worrying Rift
In separate phone calls to Foreign Minister Mohammad Javad Zarif on Sunday and Zarif's Saudi counterpart Adel al-Jubeir the following day, Ban deplored the attack on the Saudi Embassy and voiced concerns over the consequences of the rupture in Tehran-Riyadh ties, his spokesperson said.
"The secretary-general reiterated that the attack on the Saudi Embassy in Tehran was deplorable, but added that the announcement of a break in Saudi diplomatic relations with Tehran was deeply worrying. Regarding Yemen, the secretary-general urged Saudi Arabia to renew its commitment to a ceasefire," Reuters quoted Stephane Dujarric as telling reporters.
"The secretary-general urged both foreign ministers to avoid any action that could further exacerbate the situation between the two countries and in the region as a whole."
Dujarric said Ban wanted to ensure that both Iran and Saudi Arabia continue their commitment to ending the conflicts in Syria and Yemen, where the two countries back opposing sides.
"(The UN) will be pushing forward and very much hoping that the current tensions will not impact negatively on the two peace processes," he said.
UN Syria mediator, Staffan de Mistura, is visiting Saudi Arabia and Tehran this week on a preplanned visit, while UN Yemen mediator, Ismail Ould Cheikh Ahmed, is to return to the region on Thursday, Dujarric said.
"Mr. de Mistura believes that the crisis in Saudi-Iranian relations is a very worrisome development and he stresses the need to ensure that it does not cause a chain of adverse consequences in the region," he said.
In another development, the UN Security Council released a statement, urging the two sides to "maintain dialogue and take steps to reduce tensions in the region".
The statement censured the assault on Saudi missions, calling on Iran "to protect diplomatic and consular property and personnel".
