Supporters of Hosni Mubarak are clashing in central Cairo with opponents of the ousted Egyptian leader.
Several hundred people from the rival sides are separated along a main boulevard in the western half of the city by riot police. Some are hurling rocks, and police say 20 people have been injured.
The demonstration by around 100 Mubarak supporters began Friday afternoon and turned violent around midnight as angry onlookers challenged them.
One side shouted, "We love you, Mr. President," and the other side screamed back, "The people want to execute the butcher."
The 83-year-old Mubarak is to face trial in August on charges he ordered the killings of protesters during the 18-day uprising that ousted him on Feb. 11. A conviction could carry the death penalty.