CAIRO — A long night of political bloodshed in Egypt left at least 12 people dead on Tuesday, wounded 86 and seemed to dispel any notion that the military’s ouster of President Mohamed Morsi nearly three weeks ago would quickly provide the security that Egypt’s generals covet.

The death toll was the highest in a single stretch since July 8, when at least 62 people were killed by gunfire from soldiers and police officers who shot at a group of Mr. Morsi’s supporters.

Images of the latest fighting between Mr. Morsi’s supporters and opponents, which began on Monday, were jarring. Civilians, including a well-known actor, were seen firing weapons during running battles near Cairo landmarks.