No fewer than 95 people have been killed by two bomb explosions near the tomb of Iranian General Qasem Soleimani on the fourth anniversary of his assassination by the US, Iran’s state media report.
Scores of others were wounded when the blasts hit a procession near the Saheb al-Zaman mosque in the city of Kerman.
Videos showed bodies on a road and ambulances rushing to the scene.
Iran’s Supreme Leader, Ayatollah Ali Khamenei, vowed the “terrorist attack” would be met with a “harsh response”.
There were no immediate claims from any groups for what is believed to have been the deadliest such attack in Iran in 42 years.
The number of dead had initially been reported as 103, but Iran’s health minister said some names were accidentally registered twice.
Suspicion may fall on Arab separatists and Sunni jihadist groups like Islamic State (IS), who have carried out attacks on civilians and security forces in the country in recent years.
Soleimani was seen as the most powerful figure in Iran after the supreme leader before he was killed in a US drone strike in neighbouring Iraq in 2020.
Wednesday’s attack comes amid heightened tensions in the region after the deputy leader of the Iran-backed Palestinian group, Hamas, was killed in an apparent Israeli drone strike in Lebanon.
Footage broadcast by Iranian state TV showed large crowds were taking part in a procession along a road lined with banners featuring Qasem Soleimani when the explosions happened.
People could be heard screaming and then seen running away in panic after one of the blasts.
Iranian media reported the first bomb was detonated around 15:00 local time (11:30 GMT), about 700m (2,300ft) from the Garden of Martyrs cemetery around the Saheb al-Zaman mosque, in the eastern outskirts of Kerman.
The second bombing took place about 15 minutes later, around 1km away from the cemetery, targeting people who had fled the first, they said.
Kerman province’s governor told state news agency Irna that both blasts happened outside security checkpoints and that authorities were sure they were caused by bombs. But he said it was not yet clear whether they were detonated remotely or by suicide attackers.
The hard-line Tasnim news agency, which is affiliated with Iran’s Revolutionary Guards, earlier cited sources as saying that “two bags carrying bomb” were apparently detonated “by remote control”.
“We were walking towards the cemetery when a car suddenly stopped behind us and a waste bin containing a bomb exploded,” a witness was quoted by Isna news agency as saying.
“We only heard the sound of the explosion and saw people falling.”
Iran’s health minister, Bahram Eynollahi, said as well as the 95 killed, 211 people were wounded by the blasts, with 27 in a critical condition.
The Iranian Red Crescent said the dead included at least one paramedic who was sent to the scene of the first explosion and was hit by the second.
Interior Minister Ahmad Vahid said the second blast killed and wounded the most people, and that an investigation had been launched to determine who was behind the attack.
On Wednesday evening, Ayatollah Ali Khamenei issued a statement expressing his condolences to the families of those killed.
“The evil and criminal enemies of the Iranian nation once again created a disaster and martyred a large number of dear people in Kerman,” he said.
“Be it those with innocents’ blood on their hands or those corrupt minds that led to this atrocity, they will be met with firm crackdown and fair punishment, commencing immediately,” he added. “They should know that this disaster will have a harsh response, God willing.”
President Ebrahim Raisi called the bombings a “cowardly act” carried out by “Iran-hating criminals and the henchmen of terror and darkness”.
The former British ambassador to Iran, Rob Macaire, told the BBC that it was not clear who was behind the bombings.
“There are clearly opposition groups who have the ability, albeit quite constrained, to carry out violent attacks,” he said. “I don’t think they are regime-threatening attacks, but it will certainly raise the temperature.”
UN Secretary General António Guterres strongly condemned the attack and expressed his “deep condolences to the bereaved families and the people and the government” of Iran, his spokesman said.
The EU said it condemned the bombing “in the strongest terms” and expressed its “solidarity with the Iranian people”, while Russian President Vladimir Putin called the attack “shocking in its cruelty and cynicism”.
The leader of Lebanon’s Hezbollah movement – a powerful armed group that like Hamas is backed by Iran – said the victims were “martyrs who died on the same road, cause and battle that was led by” Soleimani.
As commander of the Revolutionary Guards’ overseas operations arm, the Quds Force, Soleimani was an architect of Iranian policy across the region.
He was in charge of the Quds Force’s clandestine missions and its provision of guidance, funding, weapons, intelligence, and logistical support to allied governments and armed groups, including Hezbollah and Hamas.
Then-US President Donald Trump, who ordered the 2020 drone strike, described Soleimani as “the number-one terrorist anywhere in the world” and alleged that troops under his command had murdered hundreds of American civilians and servicemen over the previous two decades.
Iran’s government accused the US of an act of international terrorism and issued arrest warrants for Mr Trump and other officials.