There are few analogues in history for the size, scale and import of the funeral that Iran’s government is preparing to hold for its slain supreme leader, Ayatollah Ali Khamenei.

Starting Friday in the capital Tehran, and running for nearly a week, with ceremonies planned in at least five cities across Iran and Iraq, the funeral is expected to draw tens of millions of people, government officials have said.

Perhaps more striking than the funeral’s complexity and scope is its symbolism at this moment. It comes more than four months after Mr. Khamenei was killed in February at the outset of the U.S.-Israeli war on Iran, and six months after Iran was gripped by nationwide protests calling for an end to his government.

While millions of mourners are expected to turn out next week, many Iranians remain deeply dissatisfied with what Mr. Khamenei’s reign brought to their country over nearly four decades of authoritarian rule. He oversaw brutal repression, including the imprisonment, torture and killing of dissidents, and presided over widening corruption and the increasing control of much of Iran’s wealth by its security forces.

When it became clear that he had been killed, some in Iran celebrated openly, at great risk to themselves.

Mr. Khamenei was not only Iran’s head of state. As the leader of its theocratic system, he also presented himself as an authoritative Shiite Muslim cleric, with devoted followers across Iraq, Lebanon, Pakistan and other countries with Shiite populations. And he commanded the Islamic Revolutionary Guards Corps, an ideological military force that has backed Shiite militant groups, like Hezbollah, across the Middle East.

Iran’s president, Masoud Pezeshkian, urged Iranians “of every ethnicity, religion, preference, and political tendency” to attend the funeral, explicitly tying their turnout to the image the country wants to present on the world stage.

“Your widespread presence will be a decisive response to the logic of terrorism, violence, and bullying, and a clear message to the world that the Iranian nation stands united and in solidarity in defending its independence and dignity,” Mr. Pezeshkian said in a statement on Thursday.

It is highly unusual in Muslim culture for burial to be delayed for so long after death. That in itself was an indicator of the extraordinary circumstances that Iran faced after Mr. Khamenei’s death, amid weeks of heavy bombardment. Officials have denied rumors that Mr. Khamenei’s body was temporarily buried and have said that it was kept in accordance with religious requirements.

Now, Iran’s government is seeking to present the funeral as a moment of national unity and shared grief, a display of bureaucratic competence and a show of resistance against an outside enemy. The emblem of the funeral, shared by the official planning body, is Mr. Khamenei’s closed fist alongside a slogan: “We must rise.”

The ceremonies will also be an opportunity for the government to demonstrate Iran’s regional influence and transnational religious ties, with plans for large-scale mourning events in Iraq, which also has a large population of Shiite Muslims and is home to Shiite militias backed by Iran.

The scale of the preparations “reflects the regime’s effort to turn Khamenei’s death into a carefully choreographed display of continuity rather than a moment of uncertainty,” said Saeid Golkar, a professor at the University of Tennessee at Chattanooga, who has researched Iran’s government and its security forces.

One challenge to that display of continuity is the fact that Mr. Khamenei’s successor, his son Ayatollah Mojtaba Khamenei, has yet to be seen in public since he was chosen as supreme leader in March. It’s still unclear whether he will appear publicly at the funeral.

The event presents an enormous logistics challenge for organizers. Tehran, is expected to come to a complete standstill, with an official holiday declared there for three days starting Saturday.

City officials have planned massive parking lots outside the capital where travelers coming from around the country can leave their cars and take buses into the city. Military barracks and schools are being used to host mourners. At a major prayer hall complex, the Grand Mosalla, where Mr. Khamenei will initially lie in state, crews are working to build platforms and build entry and exit routes for the enormous crowds expected to come and see the body.

“Mass participation is meant to project legitimacy, discipline, and popular attachment to the revolution and its leader, even if the reality of Iranian society remains far more divided and contested,” Mr. Golkar said.

The funeral ceremony, including a procession of the body through some of Tehran’s most important streets, will take place in the capital on Monday, after which another ceremony will be held for him in Qom, Iran’s center of religious learning.

On Wednesday, officials will take Mr. Khamenei’s body to Iraq, where ceremonies are planned in the cities of Karbala and Najaf, sites of pilgrimage for Shiites around the world.

“Iran will hope to reaffirm the transnational character that has defined the Islamic republic and its foreign policy,” said Afshon Ostovar, an associate professor at the Naval Postgraduate School in California, and an expert on Iranian security issues.

For the Islamic Revolutionary Guards Corps, “this will be a way of symbolizing Iran’s regional influence and power,” Mr. Ostovar added.

And on Thursday, Mr. Khamenei’s body will be laid to rest in Mashhad, his hometown, at a shrine devoted to one of the most important figures in Shiite Islam, Imam Reza.

His burial there, Mr. Ostovar said, “will be a testament to the status he holds inside Iran’s regime and among its supporters. It won’t reflect how he was seen by the Iranian people.”

Mr. Khamenei’s predecessor, Ayatollah Ruhollah Khomeini, the founder of Iran’s theocracy and leader of its 1979 revolution, was interred in a dedicated mausoleum, now a site of pilgrimage for devoted followers. By burying Mr. Khamenei in an existing shrine, albeit the most important one in Iran, the government can avoid any unflattering comparisons between the two men’s followings.

Simply providing security and crowd control over the coming week is likely to be daunting, with officials mindful of what happened two previous times towering regime figures were laid to rest: the 1989 burial of Mr. Khomeini and the 2020 burial of Qassem Soleimani, a general in the Revolutionary Guards, who was killed by an American strike.

At Mr. Khomeini’s funeral, chaotic scenes played out as an estimated three million mourners came out to pay their respects. At one point, his body fell out of a flimsy wooden coffin and was set upon by a frenzied crowd, which had to be dispersed by soldiers firing warning shots. Eight people were trampled to death that day.

And at Mr. Soleimani’s funeral, dozens of people were killed in a stampede.

Mr. Khomeini’s death in 1989 was the end of the first chapter of the Islamic republic, and launched Mr. Khamenei’s 37-year rule.

Now, the latter’s days-long, spectacle-filled funeral, Mr. Ostovar said, “will mark the end of one period of the Islamic republic’s evolution, and the beginning of a new one.”

Farnaz Fassihi contributed reporting.