At least 42 people were killed on Monday during an attack on supporters of ousted Egyptian president Mohamed Morsi outside an elite army base in Cairo, a senior medical official said.
The death toll is 42 dead and 322 wounded," Ahmed al-Ansari, the deputy head of emergency services, told AFP.
Witnesses, including Brotherhood supporters at the scene, said the army fired only tear gas and warning shots and that "thugs" in civilian clothes had carried out the deadly shooting.
Egypt's Muslim Brotherhood called for an "uprising" on Monday after its supporters were killed demonstrating against last week's military coup outside an elite Cairo army base.
It urged "the international community and international groups and all the free people of the world to intervene to stop further massacres ... and prevent a new Syria in the Arab world."
Earlier, the Egyptian armed forces said "armed terrorists" had tried to storm the headquarters of the elite Republican Guard, where the Brotherhood had been protesting, leaving one security officer dead and six critically wounded.