A United Nations (UN) spokesman on Friday called for exercising restraint and avoiding escalation in the Middle East region following the assassination of top Iranian nuclear scientist Mohsen Fakhrizadeh.

"We have noted the reports that an Iranian nuclear scientist has been assassinated near Tehran today. We urge restraint and the need to avoid any actions that could lead to an escalation of tensions in the region," Farhan Haq, the deputy spokesman for UN Secretary-General Antonio Guterres, said when responding to a question related to the assassination.

In a letter to UN Secretary-General Antonio Guterres and Inga Rhonda King, president of the Security Council for the month of November, Iran's permanent representative to the United Nations Majid Takht Ravanchi expressed strong condemnation against the "criminal assassination" of its nuclear scientist. 

He added Iran "expects the secretary-general of the United Nations and the Security Council to strongly condemn this inhumane terrorist act and take necessary measures against its perpetrators."

Iranian high-ranking nuclear physicist Fakhrizadeh, dubbed the "father of the Iranian bomb," was assassinated near capital Tehran on Friday by "armed terrorists," Iran's Ministry of Defense announced.

The Iranian government suspects that the assassination was performed by Israel's Mossad intelligence agency, though Tel Aviv has neither confirmed nor denied the allegation, according to media reports.