Security forces in Iran have fired live bullets directly into crowds of protesters, eyewitnesses say, resulting in hundreds of deaths during recent nationwide demonstrations. Omid, a protester from southern Iran, said, "I saw it with my own eyes - they fired directly into lines of protesters, and people fell where they stood." He described fighting "a brutal regime with empty hands." The BBC received similar reports following mass protests against economic troubles that escalated after calls by exiled royal Reza Pahlavi. Internet access in Iran has been cut, hampering independent reporting. On Friday, witnesses from Tehran and nearby cities described violent clashes where security forces and paramilitary Basij units attacked protesters with assault rifles. Unmarked cars reportedly drove into alleys, shooting at residents, killing two or three in each area. Human rights groups estimate at least 648 protesters were killed, including children, but exact numbers remain unconfirmed amid media blackouts. Iranian state media claim 100 security personnel died and portray protesters as rioters burning mosques and banks. Hospitals are overwhelmed with injured protesters, many suffering severe wounds, and reports cite bodies stacked in mortuaries and mass burials. United Nations officials expressed shock over the excessive use of force and called for restraint. UN Secretary-General António Guterres said he was "shocked by reports of violence and excessive use of force by the Iranian authorities against protesters." The harsh crackdown appears linked to Supreme Leader Ali Khamenei’s vow that "The Islamic Republic will not back down."