Ayatollah Ali Khamenei (C) leads a prayer over the flag-draped coffins of Ebrahim Raisi and his companions during a funeral ceremony for them at the Tehran University campus on Wednesday. AP

Iran's supreme leader presided over a funeral on Wednesday for the country's late president, foreign minister and others killed in a helicopter crash, as tens of thousands later followed a procession of their caskets through the capital, Tehran.

Ayatollah Ali Khamenei held the service at Tehran University, the caskets of the dead draped in Iranian flags with their pictures on them. On the late President Ebrahim Raisi's coffin sat a black turban — signifying his direct descendance from Islam's Prophet Muhammad (PBUH).

"Oh Allah, we didn’t see anything but good from him,” Khamenei said in his prayer in Arabic, the language of Islam's holy book, the Quran. He soon left and the crowd inside rushed to the front, reaching out to touch the coffins. Iran's acting president, Mohammad Mokhber, stood nearby and openly wept during the service.

People then carried the coffins out on their shoulders.

In attendance were top leaders of Iran's paramilitary Revolutionary Guard, one of the country's major centers. Also on hand was Ismail Haniyeh of Hamas, the militant group that Iran has armed and supported during the ongoing Israel-Hamas war raging in the Gaza Strip. Before the funeral, an emcee led the crowd in the chant: "Death to Israel!”

"I come in the name of the Palestinian people, in the name of the resistance factions of Gaza ... to express our condolences,” Haniyeh told those gathered.

Members of the Iran's Assembly of Experts listen to the country's national anthem in Tehran, Iran, on Tuesday. AP

The Muslim world "must fulfil their obligations to the Palestinians to liberate their land," Haniyeh said, recounting Raisi's words. He also described Raisi calling the Oct.7 attack that sparked the war, which saw 1,200 people killed and 250 others taken hostage, as an "earthquake in the heart of the Zionist entity.”

Also expected to attend services in Tehran were Pakistan's Prime Minister Shahbaz Sharif and a delegation from the Taliban of Afghanistan, including their Foreign Minister Amir Khan Mutaqqi.

Mourners attend the funeral procession of Ebrahim Raisi in Tehran on Wednesday. AFP

The caskets of the eight killed will then be taken on a procession through downtown Tehran to Azadi, or "Freedom,” Square — where President Ebrahim Raisi gave speeches in the past.

Iran’s theocracy declared five days of mourning over Sunday's crash, encouraging people to attend the public mourning sessions. Typically, government employees and schoolchildren attend such events en masse, while others take part out of patriotism, curiosity or to witness historic events.

A picture of late President Ebrahim Raisi (centre) is seen on a casket during a funeral ceremony in Tehran. AFP

Whether Raisi, Foreign Minister Hossein Amirabdollahian and others draw the same crowd remains in question, particularly as Raisi died in a helicopter crash, won his office in the lowest-turnout presidential election in the country’s history and presided over sweeping crackdowns on all dissent.

Prosecutors already have warned people over showing any public signs of celebrating his death and a heavy security force presence has been seen on the streets of Tehran since the crash.

Raisi, 63, had been discussed as a possible successor for Iran’s supreme leader, the 85-year-old Khamenei. His death now throws that selection into question, particularly as there is no heir-apparent cleric for the presidency ahead of planned June 28 elections.