Iranian President Ebrahim Raisi on Monday replaced a key ally from his position as the head of the country's top security body.
Ali Shamkhani had led the Supreme National Security Council for a decade and played a key role in the country's landmark rapprochement with Saudi Arabia in March.
He previously served as Iran's defense minister under two-term reformist president Mohammad Khatami from 1997 to 2005.
Replacement tapped from Revolutionary Guards
The 67-year-old Shamkhani's replacement is a former Revolutionary Guards general.
"Ali Akbar Ahmadian was appointed as the secretary of the Supreme National Security Council by the decree of the president," the official presidential website reported.
Ahmadian, who studied at the National Defence University, was previously in charge of the strategic center of the Islamic Revolutionary Guard Corps.
He was also a member of the Expediency Council, which serves as an advisory board to supreme leader Ayatollah Ali Khamenei.
Ahmadian has also previously served as commander of the Revolutionary Guards' naval forces and the head of the Guards' joint staff, the presidential website added.
Trusted diplomat who helped ease regional tensions
Shamkhani, an ethnic Arab who also previously served as a Revolutionary Guards commander, was credited with defusing Iran's yearslong tensions with several Gulf nations.
Seen as the only ethnic Arab Iranian in such a senior position in the Shi'ite-dominated country, Shamkhani inked a China-brokered deal with Saudi Arabia that ended years of rivalry.
The decree, reported by the state-run IRNA news agency, offered no explanation for Shamkhani's departure. But he had been linked to an alleged British-Iranian spy recently executed.
An Iranian insider said the change was unlikely to have an impact on the agency's policies and that Shamkhani might be considered for a "more important position."
Iran is due to hold its parliamentary election in February.
Analysts believe the turnout will be low amid mounting political dissent and growing economic hardships.
The country launched a violent clampdown on mass protests that erupted after the death of a 22-year-old Iranian Kurdish woman while held in custody by the morality police.
