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Iran's controversial President Ebrahim Raisi, Foreign Minister Hossein Amir-Abdollahian and other officials were confirmed dead on Monday after their helicopter crashed in a mountainous region of the country’s northwest, Iranian state media reported.

The death of Raisi, nicknamed the "Butcher of Tehran" for his oversight of mass executions of political prisoners in 1988, forced Iran's Supreme Leader Ayatollah Ali Khamenei to install interim leadership for Iran's executive branch. An Israeli official denied to Reuters the country had any involvement in the deadly crash, saying, bluntly, "it wasn't us."

Iran for years has backed the terror group Hamas, currently engaged in its monthslong war with Israel.

Iranian State TV said Monday that there was "no sign of life" at the crash site of the helicopter that was carrying 63-year-old Raisi, 60-year-old Abdollahian and other officials after it made a "hard landing" on Sunday.

IRANIAN PRESIDENT EXPERIENCES 'HARD LANDING' IN HELICOPTER: IRANIAN MEDIA

Iran helicopter crash site

In this photo provided by Moj News Agency, rescue team members work at the scene of a crash of a helicopter carrying Iranian President Ebrahim Raisi in northwestern Iran on Monday. (Azin Haghighi, Moj News Agency via AP)

The crash site was across a steep valley, according to state media, which added that the incident happened "due to technical failure."

Raisi was returning to Tehran on Sunday after traveling to Iran’s border with Azerbaijan to inaugurate a dam with Azerbaijan’s President Ilham Aliyev when the crash happened in the Dizmar forest in Iran’s East Azerbaijan province.

IRNA said the crash killed eight people in all, including three crew members aboard the Bell helicopter, which Iran purchased in the early 2000s.

Helicopter carrying Iranian President Ebrahim Raisi

There was "no sign of life" reported Monday at the crash site of the helicopter that was carrying Iran's President Ebrahim Raisi and other officials, according to Iranian state media. (Ali Hamed Haghdoust/IRNA via AP)

Iranian officials have said the mountainous, forested terrain and heavy fog impeded search-and-rescue operations, which began on Sunday.

The president of the Iranian Red Crescent Society, Pir-Hossein Koulivand, said 40 search teams were on the ground despite "challenging weather conditions." Because of the bad weather, it was "impossible to conduct aerial searches" via drones, Koulivand said, according to IRNA.

As the sun rose on Monday, rescuers spotted the helicopter from a distance of roughly 1.25 miles, Kolivand told state media. The officials had been missing for more than 12 hours before the helicopter was located.

Iranian Foreign Minister Hossein Amir-Abdollahian (L) and Iran's President Ebrahim Raisi (R)

Iranian Foreign Minister Hossein Amir-Abdollahian, left, and Iran's President Ebrahim Raisi attend a bilateral agreement signing in Havana, Cuba, at the Revolution Palace on June 15, 2023. (Yamil Lage/AFP)

One local government official described what happened as a "crash," while others referred to it as a "hard landing" or an "incident."

"The esteemed president and company were on their way back aboard some helicopters and one of the helicopters was forced to make a hard landing due to the bad weather and fog," Interior Minister Ahmad Vahidi said in comments aired on state TV.

Supreme Leader Ali Khamenei later confirmed First Vice President Mohammad Mokhber as interim head of the country's executive branch following the crash.

The incident comes as Iran, under Raisi and Khamenei, launched an unprecedented drone-and-missile attack against Israel last month.

WHAT HAPPENS IN THE EVENT OF RAISI'S DEATH? AN IRAN EXPERT WEIGHS IN

Iran helicopter crash search team

Rescue team members search for the wreckage of the helicopter carrying Iranian President Ebrahim Raisi in Iran on Monday. (Azin Haghighi, Moj News Agency via AP)

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Iran has also faced years of mass protests against its Shiite theocracy in response to a struggling economy and attacks on women's rights.

Fox News Greg Norman and The Associated Press contributed to this report.