U.S. Says It Believes ISIS Was Behind Bombing That Killed Dozens in Iran

American officials believe that Wednesday’s bombing attack in Kerman, Iran, was most likely the work of the Islamic State — a preliminary assessment based on intelligence, according to four American officials, who cautioned that no final conclusions have been drawn.

Two regional military officials also said they believed the Islamic State had perpetrated the attack, which killed 84 people during a memorial ceremony at the tomb of Maj. Gen. Qassim Suleimani, who was assassinated four years ago in an American drone attack.

Some Iranian leaders initially appeared to blame Israel for the attack, but the American officials said early intelligence assessments indicated that Israel was not behind the explosions. Although Israel is believed to have regularly carried out covert operations in Iran, they have typically been targeted operations against specific individuals, Iranian scientists or officials, or strikes to destroy nuclear or weapons facilities.

The American officials, who spoke on the condition of anonymity to discuss intelligence matters, cautioned that their assessment on the bombings could evolve.

Iran held a national day of mourning on Thursday to honor victims of the twin explosions, which occurred not only at a tense moment in the Middle East, but also on a highly symbolic day for some Iranians — the fourth anniversary of General Suleimani’s death. General Suleimani, the powerful military leader regarded as a malign force in the West, is revered among many Iranians, especially those who support the government.

Iranian officials had put the death toll for the two blasts at 103 on Wednesday. But the interior minister, Ahmad Vahidi, said on Thursday that 84 had been killed, according to Tasnim, a semiofficial news agency.

Speaking during a visit to a hospital that was treating people wounded in the explosions, Mr. Vahidi said the death toll might rise again because of the grave condition of some of the injured. A total of 284 were wounded in the attack, including 220 still hospitalized in Kerman, many of whom were in stable condition or requiring minor surgeries, he said, according to Tasnim.

Iran’s leaders continued denouncing what they called a terrorist attack and promising to punish the perpetrators. But they had not, so far, escalated their rhetoric against Israel.

“The blind and spiteful act was to induce insecurity in the country and take revenge on the love and devotion of the great nation of Iran, especially the zealous young generation, to the martyr Qassim Suleimani,” read a Thursday statement from the Islamic Revolutionary Guards Corps, according to Fars, another semiofficial news agency. The Revolutionary Guard Corps is the powerful military-security apparatus where General Suleimani was a top leader.

Six Israeli officials, who spoke on the condition of anonymity to discuss such intelligence matters, strongly denied that Israel had any role in the attack.

If the Islamic State was behind the bombing in Iran, it would represent a bloody resurgence for the group, which has been decimated by years of attacks from an American-led coalition in the region.

American officials said that if the Islamic State did turn out to have been responsible, it was unlikely that the group’s intention was to frame Israel for the bombings or set off a wider war. Instead, it could have been seizing an opportunity to hit an enemy: The Islamic State, a Sunni Islamist group, has long been opposed to Iran, which has a Shiite Islamic government.

The group has claimed responsibility for several previous attacks on Iran, including most recently in October 2022, when a gunman killed 13 people at a shrine in the city of Shiraz.

Mick Mulroy, who served as a Pentagon official in the Trump administration, said the Islamic State could have carried out the attack, because it has “no love lost” for Iran. “But it does seem like an odd time to launch an attack with the current conflict in Gaza and the unified Muslim support for the Palestinians,” he said.

Colin P. Clarke, a counterterrorism analyst at the Soufan Group, a security consulting firm based in New York, said he suspected the Islamic State’s Khorasan affiliate, also known as ISIS-K, as a likely perpetrator of the attack.

“ISIS-K has demonstrated both intent and capability to attack targets inside Iran proper,” Mr. Clarke said. “ISIS-K wants to attack Iran, because Tehran is the most prominent Shia power and the ire of ISIS-K’s highly sectarian agenda. More so than other ISIS branches, ISIS-K propaganda continuously focuses on denigrating Shia as apostates.”

Mr. Clarke said the attack at the commemoration ceremony, a highly symbolic and sectarian target given General Suleimani’s stature as the architect of the Tehran-led Shiite axis in the region, fit the group’s method of attacks.

But even if Israel — one of Iran’s longtime archenemies — is not responsible, Iran “is likely to get a lot of propaganda mileage out of either directly blaming the Israelis” or letting Iranians believe that Israel was responsible, Mr. Clarke said.

Tasnim, the news agency, reported that the first explosion occurred at 3:04 p.m. Wednesday as people crowded the road leading toward General Suleimani’s tomb. The second blast came 13 minutes later, it said.

Another semiofficial news agency, IRNA, quoted a police spokesperson as saying that three police officers had been killed in the explosions while trying to help other victims.

The commemoration ceremony was held to mark the fourth anniversary of General Suleimani’s assassination in an American drone strike at Baghdad airport in January 2020. Similar ceremonies honoring the general are held annually.

Leily Nikounazar, Eric Schmitt and David E. Sanger contributed reporting.