Eight people were killed in clashes between pro-reform protesters and security forces in Iran yesterday, according to an Iranian opposition website. Among the dead was the nephew of the opposition leader and defeated presidential candidate Mir Hossein Mousavi. State television confirmed Ali Habibi Mousevi's death. He was killed by "unknown assailants", Press TV reported. Yesterday's killings, reported by the opposition Jaras website, plunged Iran into a volatile and dangerously unpredictable new phase in the six-month-old showdown between the regime and an emboldened and increasingly angry opposition. The demonstrations were the fiercest in Tehran since the immediate aftermath of June's disputed presidential election, trapping the flailing authorities in a Catch-22 situation. They could also provoke further street protests against the government of Mahmoud Ahmadinejad. Unable to instil paralysing fear into the opposition, the regime increased the stakes by fulfilling its threats a "merciless" response to continued demonstrations. They had been reluctant to create martyrs, which would lead to a new cycle of mourning and mass protests. But fear trumped caution yesterday as the regime responded to mass demonstrations by inflicting the heaviest casualties in months. An adviser to Mr Mousavi confirmed that the opposition leader's nephew was killed. "I express my regrets and deep condolences over the martyrdom of your nephew Ali Habibi Mousevi on Sunday," Kaleme website quoted Alireza Beheshti as saying. Jaras said at least four protesters were killed and many others wounded in the north-western city of Tabriz, a Mousavi stronghold. A witness told Reuters that people were pouring into the streets of Tabriz, chanting anti-government slogans. "We will kill those who killed our brothers," Jaras quoted demonstrators as chanting. The deaths came on a day of huge emotional, symbolic and political resonance as protesters commemorated Ashura, which marks the death in the year 680 of Imam Hossein, a grandson of the Prophet Muhammad and the faith's quintessential martyr. Vastly outnumbered, his small band of acolytes confronted the forces of oppression and injustice of his day - the uncanny parallel is not lost on today's opposition or the regime. Yesterday's protests spread well beyond the capital, reflecting the opposition's growing strength nationwide and across social boundaries. The few foreign reporters allowed to stay in Iran were ordered to remain in their offices while the authorities attempted in vain to black out news of the damaging events. But the tech-savvy opposition soon flooded the internet with mobile phone, camera and video footage showing the scale of their protests and the violent response of the security forces. Photographs from the clashes showed one man whose face was covered in blood, lying on the ground. Other pictures showed burning motorbikes and protesters throwing stones at police. The reported killings would be the first in street protests since widespread unrest in the immediate aftermath of the June poll in which the opposition says more than 70 people died. The authorities have estimated the post-vote death toll at about half that number, including pro-government militiamen. The Tehran police chief, Azizollah Rajabzadeh, speaking about yesterday's protests, said: "So far there have been no reports of killings and no one has been killed up to now," according to the ISNA news agency. He said some arrests had been made. Tens of thousands of demonstrators had packed the streets of Tehran and clashes also erupted in the cities of Shiraz, Isfahan, Najafabad, Mashhad and Babol, Jaras said. It said 20 people were detained in Qom and Mashhad. Shots were heard in northern Tehran after nightfall. English-language state television reported sporadic clashes in Tehran and said a bank and bus stop were set ablaze. It said police had fired into the air to disperse demonstrators. The official IRNA news agency said two women and a child were hurt when rioters threw stones at people marking Ashura. The semi-official Fars News Agency said supporters of Mr Mousavi "followed the call of the foreign media" and took to the streets, a reference to the government position that the unrest is being stoked by foreign enemies of the republic. It said the group of "deceived hooligans" damaged public and private property and "disrespected" Ashura, without elaborating. Despite scores of arrests and security clampdowns, opposition protests have flared repeatedly since the June poll, which the opposition said was rigged to secure Mr Ahmadinejad's re-election. Reformist websites said there had also been clashes in Tehran on Saturday, with baton-wielding riot police firing tear gas and warning shots to disperse Mousavi supporters. The authorities had warned the opposition against using Tasoua and Ashura festival to revive protests against the clerical establishment. "The Iranian nation has shown tolerance so far but they should know that the system's patience has a limit," said Mojtaba Zolnour, a representative of Supreme Leader Ayatollah Ali Khamenei in the Revolutionary Guards, Fars reported. This year's Ashura yesterday coincided with the traditional seventh day of mourning for leading dissident cleric Grand Ayatollah Hossein Ali Montazeri, who died a week ago at the age of 87 in the holy Shiite city of Qom. A spiritual patron of Mr Mousavi's movement, he was a fierce critic of the hardline clerical establishment. The unrest that erupted after the June vote is the biggest in the Islamic state's 30-year history. Authorities deny opposition charges that voting was rigged. The turmoil has complicated the international dispute over Iran's nuclear programme, which the West believes may have military ends, not just civilian purposes. Iran has rejected an end-of-year deadline set by world powers for it to agree a UN-drafted deal to ship most of its low-enriched uranium abroad in exchange for fuel for a Tehran research reactor. It has also set back tentative US moves towards a rapprochement with Iran initiated by the US President Barack Obama when he took office in January. mtheodoulou@thenational.ae * With additional reporting by Reuters