At least 648 protesters have been killed in the crackdown by Iranian security forces on a protest movement that has shaken the Islamic republic, Norway-based Iran Human Rights (IHR) said Monday, warning the actual toll could be far higher.For all the latest headlines follow our Google News channel online or via the app.“The international community has a duty to protect civilian protesters against mass killing by the Islamic republic,” said IHR director Mahmood Amiry-Moghaddam, commenting on the new tally of deaths that have been verified by the NGO.IHR said that “according to some estimates more than 6,000 may have been killed”, but warned that the almost four-day internet blackout imposed by the Iranian authorities makes it “extremely difficult to independently verify these reports.”Read more:Iran summons French, German, Italian, UK envoys over support for protests