Islamic State has claimed responsibility for Wednesday’s attack on a crowd in southern Iran marking the anniversary of the death of the senior Revolutionary Guards commander Qassem Suleimani. At least 84 people died when two blasts ripped through the crowd near Suleimani’s tomb in the city of Kerman, four years after he was killed by a US drone strike in Baghdad. Suleimani had been a staunch enemy of IS, which resents the damage he did to its cause in Iraq and Syria. Early on Thursday Iran had said it was bolstering security along its borders with Afghanistan and Pakistan, in the first tangible sign that it suspected that the attack was the work of an IS affiliate. “We have points on the border of Afghanistan and Pakistan that are a priority for blocking,” Iran’s interior minister, Ahmad Vahidi, said. Later in the day, in a statement posted on its affiliate Telegram channels, the Sunni extremist group said two IS members had detonated their explosive belts in the crowd. One of Iran’s main goals will be to limit the amount of traffic crossing the border, something that will be discussed with the Taliban. A leader of the Afghan opposition, Ahmad Massoud, had already sent a message of condolence to Iran that made clear he believed IS was involved. The group has an affiliate – Islamic State Khorasan Province – that is primarily active in Afghanistan. In a statement, the UN security council condemned what it described as a “cowardly terrorist attack” in Kerman and sent its condolences to the victims’ families and the Iranian government. The Revolutionary Guards promised a harsh response, describing the attack as a “blind and spiteful act to induce insecurity in the country and take revenge on the love and devotion of the great nation of Iran”. Iran’s first vice-president, Mohammad Mokhber, told reporters those responsible would “receive a very strong retaliatory action from the hands of Suleimani’s soldiers”. Regional tensions have surged in recent days, amid war in Gaza sparked by the Hamas attack on Israel on 7 October, which Tehran welcomed while denying any involvement. On Sunday US helicopters opened fire on Iran-backed Houthi rebels after they attacked a cargo ship in the Red Sea, killing several of them. On Tuesday an Israeli drone strike killed one of Hamas’s most senior officials in Beirut and two days later the US said it had carried out an airstrike on the logistical support headquarters of an Iran-backed militia in central Baghdad, killing a high-ranking militia commander. Early Iranian responses to the Kerman attack pointed the finger at the US and Israel. The US rejected any suggestion that it or its ally Israel were behind the deadly blasts, while Israel declined to comment. Expert opinion outside Iran said the attack bore the hallmarks of IS. Western sources said it was plausible the group sensed that the well-advertised annual anniversary pilgrimage might be overseen by security forces distracted by events elsewhere. In 2022 IS claimed responsibility for a deadly attack on a Shia shrine in Iran that killed 15 people. Earlier attacks claimed by IS include twin bombings in 2017 that targeted Iran’s parliament and the tomb of the Islamic Republic’s founder, Ayatollah Ruhollah Khomeini. Tehran often accuses its arch-enemies, Israel and the US, of backing militant groups that have carried out attacks against Iran in the past. Hospital staff in Kerman revised down the number of dead from about 100 to 84 on Thursday and said they were optimistic that the more than 200 people being treated for injuries would survive. As names of the dead were published, the health ministry said that 28 of those injured were aged under 15. Suleimani, who helped develop Iran’s regional “axis of resistance” against the US by nurturing Iranian proxy groups, has been granted a near-mythical status inside Iran since his death. There is no sign that Iran will take swift retribution for the Kerman attack. Instead, it will try to harness a wave of sympathy in the Islamic world to press its call for an end to what it regards as the US’s destabilising interventions in the Middle East. Iranian hardliners frequently praise Tehran’s “strategic patience” in seeking the long-term ousting of the US from the region, and believe Israel is trying to drag Iran into an all-out war because Israel senses this is the best way to avert US disengagement. With parliamentary elections due in the spring, and alienation from the regime widespread, the government’s handling of security is likely to grow as a domestic political issue. The former Iranian president Hassan Rouhani, a reformer and a potential candidate for the assembly of experts in the spring, sent out a coded message arguing that security “will be strengthened by acquiring legitimate freedoms, guaranteeing the fundamental rights of the nation, and employing all sympathetic forces with a national perspective”. By contrast Mahdi Mohammadi, an aide to the speaker of parliament, called for a fundamental shift as the only way to deter Israel, and criticised Rouhani for, in effect, seeking Israel’s approval.