TEHRAN, IRAN—As groups of families and others gathered Sunday evening at cafes around Niloofar Square—a middle-class area in eastern Tehran—after breaking their fast for Ramadan, a series of explosions struck the area, leveling several buildings and killing over 20 people, according to witnesses at the scene and later reports from local news sources.

Witnesses who spoke to Drop Site said two explosions hit the area—a smaller strike in the vicinity, followed by a larger one that devastated much of the neighborhood, a tactic known as a “double tap” strike that is used to inflict maximum casualties.

Videos of the immediate aftermath of the attack showed several individuals dead and wounded as well as massive destruction on the street outside. In Cafe Ahla, next to the square, blood and debris soaked the floors. Several patrons who had been sitting there when the attack struck could be seen dead on the floor or with their mutilated bodies still sprawled across their seats.