TEHRAN (AFP/Reuters) - Iranian security forces killed several protesters including Opposition leader Mir Hossein Mousavis nephew in a fierce crackdown Sunday on anti-government rallies in Tehran, websites said. Witnesses said dozens of protesters were hurt and several arrested during what turned into the bloodiest showdown between protesters and security forces since the height of unrest in June following a disputed presidential election. Opposition website Rahesabz.net said four protesters were shot dead by security forces in central Tehran while reformist website Parlemannews said Mousavis nephew died in hospital after being shot in the chest. Iranian state television reported that several people were killed in clashes in Tehran between rioters - Opposition supporters - and pro-regime forces out on the streets marking solemn Shiite Ashura ceremonies. Four people were killed and over 300 were arrested in the protests, Irans deputy police chief Ahmad Reza Radan said on state television. According to Reuters, another Opposition website said eight people were killed in clashes. In these clashes, several people from the two sides were killed and several wounded, it said, without breaking down the casualty toll. The authorities response again drew international criticism. France condemned the violent police action against simple protestors and called for a political solution, the foreign ministry said. Witnesses said police first used batons and tear-gas in the crackdown, which followed stern warnings by the authorities that they would crush attempts to use the Ashura processions as a launch pad for protests. When this failed to disperse the crowds, they opened fire, websites said. Parlemannews said Seyed Ali Mousavi, the 35-year-old nephew of Mousavi, was shot near his heart during clashes at Enghelab square and was martyred after he was taken to Ebnesina hospital. Opposition website Rahesabz.net reported four people killed but did not identify them. Three of our compatriots were martyred and two were injured in clashes. The (website) reporter who was on the scene said these three were directly shot at by military forces, A fourth protester was killed later near Vali Asr intersection on Enghelab, it said. AFP was not able to verify the various reports as the foreign media is banned from covering opposition demonstrations. Witnesses said that enraged protesters fought back against the security forces, pelting them with stones and chanting: We fight and we die to get back Iran. They beat up several policemen and set their pick-up truck on fire, witnesses said, adding that the policemen ran away with blood streaming down their faces. Rahesabz also reported heavy clashes between protesters and security forces in Isfahan and Najafabad - the home town of late cleric Grand Ayatollah Hossein Ali Montazeri - the city of Babol in northern Iran as well as in the southern city of Shiraz. It added that clashes broke out in Irans second city Mashhad and the central city of Arak and cited unconfirmed reports of casualties in Tabriz, Irans main northwestern city.