Iran sought to project a sense of order and control on Monday by quickly naming an acting president and foreign minister a day after a helicopter crash killed both leaders. The change in leadership came at a time of heightened tensions in the Middle East and domestic discontent in Iran, where many residents have called for an end to decades of repressive clerical rule.

Iran’s supreme leader, Ayatollah Ali Khamenei, announced five days of mourning for the president, Ebrahim Raisi, 63, and the foreign minister, Hossein Amir Abdollahian, 60, who died when their helicopter plunged into a mountainous area near the Iranian city of Jolfa. The men had been returning from Iran’s border with Azerbaijan after inaugurating a joint dam project.

Iran’s Armed Forces said they had created a committee to investigate the crash, which state media attributed to a “technical failure.”

Mr. Raisi, a hard-line cleric who came of age during the country’s Islamic revolution, oversaw a deadly crackdown on protesters as the head of the judiciary in 2019 and as president in 2022. He had been widely viewed as a possible successor to Ayatollah Khamenei, 85.

On Monday, Ayatollah Khamenei named Iran’s first vice president, Mohammad Mokhber, acting president and announced that Mr. Mokhber would organize elections for a new president within 50 days. A conservative political operative, Mr. Mokhber has a long history of involvement in large business conglomerates closely tied to Ayatollah Khamenei.

Iran’s cabinet appointed Ali Bagheri Kani, a deputy foreign minister, as the ministry’s “caretaker,” the IRNA state news agency reported. Mr. Bagheri Kani has served as Iran’s chief nuclear negotiator and was involved in a deal last year that freed imprisoned Americans in exchange for several jailed Iranians and eventual access to about $6 billion in Iranian funds.

Iranian officials said there would be a public procession in Tabriz, the closest big city to the site of the crash, on Tuesday and that the bodies would then be brought to Tehran for a state funeral.

Some Iranians mourned Mr. Raisi, including people who held an overnight vigil in his hometown, Mashhad, in northeast Iran. State media also showed images of vigils in Tehran and many other cities.

“Raisi was tireless,” Ayatollah Khamenei said in a statement. “In this very sad incident, the people of Iran have lost a valuable and loyal public servant.”

Mohammad Ali Ahangaran, a prominent religious scholar in Tehran, said in a telephone interview that he had cried for hours when he heard the news and said that although he had once campaigned against Mr. Raisi, the death of a president was a somber moment for the nation.

Analysts in Iran said that while there was speculation about who might be elected as the next president, there was little question about the overall stability of the country or the government. They pointed out that Ayatollah Khamenei will remain supreme leader with power over major state policies.

“The deaths have shocked everybody — even the rival political factions have all come together to express solidarity, as is customary in Iranian culture when someone dies,” Sasan Karimi, an adjunct professor and foreign policy researcher at the University of Tehran, said in a telephone interview. “In reality, there will be no real power vacuum in Iran because the cabinet and the government is in place and functioning.”

Despite the official calls for mourning, many Iranians welcomed Mr. Raisi’s death, seeing him as one of the key figures in a corrupt regime who oversaw the execution of dissidents, used brutal violence to suppress and kill protesters and arrested journalists and activists. Many of the victims were women and young people.

Over the last two years, anger at the government has also grown as Iran’s currency has plunged to a record low, water shortages have been intensified by climate change and the country was hit by the deadliest terrorist attack since the Islamic Republic was founded in 1979.

On social media, one widely circulated meme showed a helicopter being brought down by the braided hair of a young woman with her head uncovered. The image was a reference to the “Woman, Life, Freedom” protests that began in 2022, opposing a law that requires women to dress modestly and wear head scarves.

“All this humor is a bitter expression of the pain of a nation,” said Safa, 55, a doctor in Mashhad who, like other Iranians, asked to be identified only by her first name for fear of government retribution.

Parisa, 55, who lives in Lahijan, in northwestern Iran, said she had initially felt relief when she heard that the president and foreign minister had been killed in a helicopter crash.

“But after they were found, I thought this easy death wasn’t enough for them,” she said. “They should have been tried in court and forced to howl like dogs and been given long and painful punishments.”

Many countries, including the United States, offered condolences after the crash.

Iranian state television reported that President Vladimir V. Putin of Russia, a close ally of Iran, had spoken to Mr. Mokhber and had offered Russia’s assistance “in full capacity.” Turkey, Iraq and the European Union said they had also offered help in search-and-recovery efforts at the crash site.

John F. Kirby, a national security spokesman at the White House, said that the United States had offered its “condolences,” but added that “we’re going to continue to hold Iran accountable for all their destabilizing behavior in the region, which continues to this day.”

Last month, a long shadow war between Iran and Israel burst into the open with an exchange of direct strikes. Two Iran-backed militias, Hamas in the Gaza Strip, and Hezbollah in Lebanon, continue to battle Israeli forces. And the future of Iran’s nuclear program looms over the Middle East. The country has produced nuclear fuel enriched to a level just short of what would be needed to produce several bombs.

In Israel, Mr. Raisi was perceived as a figurehead who had little influence on foreign policy or Iran’s support for Hamas, Hezbollah and the Houthis in Yemen.

“From Israel’s point of view, I don’t see any achievement in his being replaced by some other radical conservative Iranian,” said Sima Shine, an analyst at the Institute for National Security Studies, a research group in Tel Aviv. “The president is not the most important person in Iran.”

Analysts said Mr. Raisi’s death could raise the prospects of the ayatollah’s son, Mojtaba Khamenei, succeeding him as supreme leader. A low-profile hard-liner, he grew up among the clerical and political elite in Iran and has close ties with the Islamic Revolutionary Guards Corps, a powerful Iranian military force.

A growing number of leaders within Iran’s political establishment have begun to publicly endorse him, said Arash Azizi, a lecturer at Clemson University who focuses on Iran.

“When people started talking about Mojtaba as a potential successor in 2009, I considered it a cheap rumor,” Dr. Azizi said. “But it’s not that anymore. It’s very clear now that he is a remarkable figure. And he’s remarkable because he’s been almost entirely invisible in the public eye.”

Other Iran experts dismissed the idea that Mojtaba Khamenei could replace his father as supreme leader, saying it would upend the logic of Iran’s system of government. For one, the son teaches at Iran’s largest seminary, but he has not achieved a high rank within the Shiite clerical hierarchy, a qualification long seen as necessary for the role of supreme leader.

Since the Islamic revolution deposed the shah in 1979, Iran has also proclaimed the end of hereditary rule as one of its foundational principles.

“If the supreme leader turns into a hereditary system, what does that mean? It means the system is dead,” said Mohammad Ali Shabani, an Iran analyst and editor of Amwaj, a news outlet based in Britain that focuses on Iran, Iraq and the Arabian Peninsula.

Until a successor is chosen, there will be intense jockeying for influence and power, analysts said. And ultimately, they said, the choice will be made from within an opaque system that has only become less transparent in recent years.

“The reality is that nobody knows,” Mr. Shabani said. “And that is crazy — there is zero transparency on a process that affects millions of Iranians.”