Memorial ceremonies for Iran's President Ebrahim Raisi and other passengers killed in a helicopter crash have been held across the country.

All eight people aboard a helicopter that went down in the northwestern Iranian province of East Azerbaijan on Sunday were killed, including Raisi and Foreign Minister Hossein Amir Abdollahian.

Authorities are working to retrieve passengers' bodies and determine the cause of the crash, which state-run media has attributed to bad weather.

Mourners packed into the venues of memorial services held in Tehran and other parts of the country on Monday.

Iran's supreme leader Ayatollah Ali Khamenei declared five days of national mourning.

Funerals are planned in locations including Mashhad, a northeastern Iranian city where Raisi came from.

Officials said First Vice President Mohammad Mokhber will take over as interim president for the time being. Elections for a new president will be held on June 28.

It remains to be seen how changes to the government lineup will affect the country's diplomatic policy in the Middle East. Iran backs Hamas militants, who are fighting Israel in Gaza.