CAIRO—A 24-hour standoff between Egyptian security forces and antigovernment protesters holed up in a Cairo mosque ended amid gunfire and explosions late Saturday afternoon, with clashes leaving at least 173 dead across the country.

Antigovernment protesters erected barricades inside the al Fatah Mosque in Cairo's Ramses Square after deadly clashes Friday afternoon had turned the mosque into a makeshift morgue and medical center and a refuge for some 400 protesters later that evening.

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