Egypt has barred the head of Human Rights Watch from entering the country ahead of the release of a report on a mass killing of protesters, HRW officials said Monday. Kenneth Roth, executive director of the New York-based NGO, and HRW Middle East director Sarah Leah Whitson were held overnight in Cairo airport before being denied entry, Whitson wrote on Twitter. "It's official - shortest visit to Cairo ever - 12 hours before deportation for 'security reasons'- the new Egypt certainly 'transitioning'," Whitson wrote. The protesters, supporters of deposed Islamist president Mohamed Morsi, had been camped out around the Rabaa al-Adawiya mosque in Cairo for weeks when police moved in to disperse them on August 14, using tear gas and live ammunition.