Four months after its supreme leader was killed in U.S.-Israeli airstrikes, Iran’s government began a week of elaborate events to mourn and bury Ayatollah Ali Khamenei, sending a message of stability and unity to the world — and to its enemies.

Images published on Friday by Iranian state media showed Iranian and foreign officials, militia members and religious leaders walking to and standing before the casket of Ayatollah Khamenei, who was killed on Feb. 28. Some visitors bowed solemnly, prayed or cried.

It sets the stage for a series of ceremonies, which will continue on Saturday with a public viewing of Ayatollah Khamenei’s casket. After a procession in Tehran on Monday, his body will be taken to holy Shiite cities in Iraq before he is buried in his hometown, Mashhad, in Iran.

The casket, decorated with the Iranian flag, was topped by a black turban and a black-and-white checked scarf like one he often wore, which in Iran is associated with the country’s Basij militia force. The black turban signifies that he was a cleric descended from the Prophet Muhammad.

Friday’s ceremony took place in Tehran’s Grand Mosalla, a large prayer complex where Ayatollah Khamenei gave many important addresses during his reign. State news reports said his casket was surrounded by those of family members who were killed along with him.

By Friday morning, symbols of mourning had spread across Tehran. Giant black banners hung from overpasses and buildings, while billboards bearing Ayatollah Khamenei’s portrait appeared along major roads and intersections.

Some showed him alone, gazing outward in the familiar official imagery that long dominated the country’s political landscape. Others paired him with his son and successor, Mojtaba Khamenei, visually linking the end of one era to the beginning of another.

While Iran’s government is seeking to portray Ayatollah Khamenei as a beloved and respected leader of global stature, many Iranians may view the expensive, dayslong funeral with discontent or anger.

Over 37 years of authoritarian rule, Ayatollah Khamenei harshly repressed dissent and allowed economic mismanagement and corruption to fester in Iran.

The long delays to his burial, more than four months after his killing, reflect the extraordinary circumstances Iran has faced this year: bombardment by the United States and Israel, with uncertainty over whether the government could ensure a secure event.

Mr. Khamenei was a constant presence in Iran’s political life for decades. Some of his supporters said that his killing remained difficult for them to process, and the days of mourning planned across the country have become an occasion to grieve and mark the end of a political era.

The funeral comes at a particularly turbulent moment for Iran. The past six months have left deep fissures in the country, with protests, regional conflict, security tensions and internet shutdowns disrupting daily life and contributing to broader uncertainty and instability. For many Iranians, the death of a leader who had dominated for decades was yet another turning point in a period defined by upheaval.

“I still cannot believe he’s gone,” said Dunya Mohamadi, 24, who was in central Tehran on Friday with her 10-month-old son, Ali. She said she had traveled with her family from Malard, about 24 miles west of the capital, to attend the ceremonies. “My heart wants to mourn as best as I can,” she said.

The New York Times was granted access to the funeral ceremonies of Ayatollah Khamenei by Iran’s government, which determined the ceremonies our reporters could attend, accompanied by a government-provided translator and a guide. The views expressed by people interviewed at these events may not be representative of many Iranians, while others may have felt unable to speak freely.

More than 50 official foreign delegations participated in the viewing ceremony on Friday, a spokesman for the funeral organizers told Iranian state media.

Dmitri A. Medvedev, a former president of Russia and the deputy chairman of its Security Council, is expected to attend Friday’s ceremony, the Kremlin spokesman, Dmitri S. Peskov, said Thursday. Russia has given support to Iran during its war with Israel and the United States, and Iran has supplied drones to Russia that it has used to attack Ukraine.

China is sending a senior Chinese lawmaker, He Wei, who is a vice chairman of its top legislature. Iran is increasingly looking to China as a critical economic partner, and the country has been the primary purchaser of Iranian oil over the last several years.

Leaders of Shiite communities abroad were also in attendance, including from Pakistan. During the six days of public ceremonies that are expected to follow, Iran’s government is seeking to emphasize Ayatollah Khamenei’s role as a Shiite spiritual leader with devoted followings throughout the Muslim world.

Members of several Iranian-aligned militias in Iraq also attended on Friday, including Kataib Hezbollah, according to images published by Iranian state media. The group has attacked U.S. targets in Iraq in recent months. The images also showed family members of slain leaders of the Lebanese militant group Hezbollah, which is backed by Iran.

Iraq’s president, Nizar Amedi, and the country’s speaker of Parliament, Haibat al-Halbousi, were also in attendance for the funeral ceremonies. The arrival of Iraqi officials comes at an awkward moment for Iraq’s new government, as it is under increasing pressure to loosen its ties to Iran.

Ayatollah Khamenei’s funeral has also brought together adversaries, if not outright enemies, who are otherwise engaged in deadly conflicts in the region.

The president of Iraq’s Kurdistan Region, Nechirvan Barzani, met with Iranian officials on Friday, according to Iranian state media. His region hosts Iran’s exiled Kurdish militias, who remain in an undeclared shadow war with Iran’s Islamic Revolutionary Guards Corps. There have been reports by local news outlets in recent days of clashes.

From Afghanistan, one of the Taliban’s most senior figures, Mullah Abdul Ghani Baradar, and its foreign minister, Amir Khan Muttaqi, were set to attend the funeral.

And on Friday, Ahmad Massoud, the son of Ahmad Shah Massoud, a commander who fought the Taliban in the 1990s, could be seen paying his respects. Mr. Massoud now leads one of the main opposition groups to Taliban rule from abroad.

Also scheduled to attend the funeral were Prime Minister Shehbaz Sharif of Pakistan and the country’s army chief, Field Marshal Syed Asim Munir. Their country has been embroiled in a conflict with Afghanistan that has left hundreds dead since late February as Pakistani officials accuse the Taliban of supporting militant groups that have killed thousands of security personnel in Pakistan in recent years.

Pakistan and Iran’s relations have been marred by tensions in recent years, but the war with the United States and Israel, and Pakistan’s role as a mediator to end the conflict, has brought their leaderships closer.

The killing of Ayatollah Khamenei rattled many among Pakistan’s estimated 35 million Shiites, a minority often targeted by militant violence.

The city of Tehran had already begun reorganizing itself on Friday for the large public elements of the funeral in the days ahead.

Officials announced traffic restrictions and heightened security measures before the procession, with police officers and security personnel visible across central Tehran. Many shops in the city center were closed, leaving the typically crowded streets unusually quiet. Roads were closed as the authorities prepared for what they said would be one of the largest public gatherings in the history of the Islamic Republic.

Across the capital, volunteers prepared stations to feed and support the large crowds expected to arrive before public ceremonies were to begin early Saturday. At one such station, Hamid Reza, 54, directed men unloading boxes of food, fruit and supplies from a truck. He said organizers at that location alone expected to distribute some 300,000 bottles of water and had stocked eggs, lentils, watermelons and snacks for mourners.

He described the work as his contribution to honoring a leader he admired.

“We miss him,” he said. “I wish I had sacrificed myself for our leader.”

Elian Peltier, Erika Solomon, Paul Sonne and Li You contributed reporting.

A Tibetan activist lit himself on fire and outside of the United Nations headquarters in New York on Thursday to protest China’s control over his homeland, declaring in a video before his self-immolation that Beijing’s policies were “destroying the Tibetan people.” He later died.

Friends of the activist identified him as Lobga Rangzen, a 52-year-old resident of Queens, originally from eastern Tibet, who had been an advocate of Tibetan independence for more than a decade.

The police said that around 6:30 p.m. on Thursday they responded to a call for help at East 42nd Street and 1st Avenue, next to the U.N. headquarters, where they found a man with severe burns throughout his body. He was taken to Bellevue Hospital, where he was pronounced dead.

Lobga Rangzen appeared to have recorded his self-immolation on a livestream on his own Facebook page, which was verified by a friend of his. In it, he could be seen walking across a street outside of the U.N. building with a large Tibetan flag. Moments after he erected the flag on a street corner, he lit himself on fire. He stepped on to the street as his body was engulfed in flames then collapsed on the ground. (The video was later taken down.)

In another video posted on his Facebook page also on Thursday, Lobga Rangzen called on his compatriots in exile to unite and do more to fight for Tibet’s independence. He hinted that he planned a demonstration that day and said that it was purely for political reasons.

“So if I do a big action today, I want you to know it is not for any personal reason. It is not because I have nothing to eat or nothing to wear, but because I am doing this for my country. For the Tibetan nation,” he said.

The protest took place a day after China implemented a new “ethnic unity” law that requires Mandarin be the main language of instruction in schools and includes other measures aimed at assimilating minorities such as Tibetans and Uyghurs into China’s mainstream Han Chinese majority.

Since 2009, there have been more than 150 self-immolations of Tibetans in China in protest of Beijing’s hard-line campaign against what it sees as Tibetan separatism. The Communist Party has placed the region of Tibet and neighboring Tibetan areas under close security, tightly controlled its monks and monasteries and emphasized the teaching of Mandarin Chinese over Tibetan.

The self-immolations in China were initially carried out by monks, but nomads, farmers and others also began staging the protest. They were so frequent that in 2012, the top human rights official at the United Nations at the time, Navi Pillay, criticized China for the suppression of Tibetan rights, saying that it had driven them to “desperate forms of protest.” Ms. Pillay appealed to Tibetans to seek other ways of expressing their feelings and urged China to allow them to do so without retribution.

Even as the self-immolations became central to the Tibetan protest movement, some Tibetans were anguished over the deaths of their young men and women and asked how the acts reconciled with Buddhist teachings. The Dalai Lama, the Tibetan spiritual leader-in-exile, has described the religious issues surrounding the self-immolations as “very, very complicated.”

Such protests have been rare in the United States, according to Tenzin Dorjee, director of research and advocacy at Tibet Action Institute, who was a friend of Lobga Rangzen’s. He said that Lobga Rangzen’s clarity and calm during his last statement suggested he had been planning this action for a while.

Tenzin Dorjee described his friend as a central member of the Tibetan community in New York, helping with cultural events and participating in countless demonstrations. “He would come to every single protest rally we ever organized,” he said.

“For him, there was no other goal or value in life that was higher than national liberation,” he said. “That was the singular thing that occupied and preoccupied him.”

According to Jamyang Norbu, a Tibetan writer and another friend of Lobga Rangzen’s, the activist was born in the Kham region of Tibet and went into exile in the 1980s. He attended a Tibetan monastery in India before moving to the United States, where he worked in construction and eventually became a cab driver.

Jamyang Norbu said that Lobga Rangzen had a brother in China who had been imprisoned.

On Thursday night, hundreds of demonstrators gathered outside of the U.N. building to commemorate Lobga Rangzen, according to Jamyang Norbu, who was at the rally. It was evidence of his friend’s popularity, as someone who frequently helped people with odd jobs.

“He was funny, he was generous,” he said of his friend.

The presence of the demonstrators embodied Lobga Rangzen’s hope that the community would unite, overcoming differences over how to deal with Beijing. Some Tibetan activists support negotiating with the Chinese government for greater autonomy, rather than full independence.

“He drew a line in the sand here today. He’s saying unless you hold out for Tibetan independence, there’s no hope at all,” Jamyang Norbu said.

Tenzin Dorjee said that the last time he spoke with the activist was by phone in June, while he was hosting a fund-raiser in Queens. Lobga Rangzen called just as the event was wrapping up, apologizing that he could not make it but asking Tenzin Dorjee to call an Uber for an elderly man who had come but did not know how to order a car.

“This is who he is, helping people all the time,” Tenzin said.

Claire Fahy contributed reporting from New York.