Violence has returned to the streets of Cairo, as protesters impatient with the slow pace of change have vented their frustration by throwing stones at police, who have responded by firing tear gas into the crowds.

In a grim reminder of previous protests in which more than 800 people were killed, the Health Ministry reported that more than 1,000 people were injured in the fracas, including 40 members of the police. No deaths have been reported. A state news agency reported the arrests of 40 people.

Families of those killed in the February uprisings had a ceremony to honor their lost loved ones. Anger fueled a march to Tahrir Square and the Interior Ministry, and police were dispatched to keep the peace. Some in the crowd lit tires. Amid the black smoke, some threw rocks at police. The response was tear gas.

The military council ruling the country issued a statement calling for calm in the streets, but the people in those streets were more interested in speeding up the promised changes and seeing more former members of the government of President Hosni Mubarak brought to justice.

Several top government officials have been convicted of serious crimes, but the trial for Mubarak himself is still a month away. (In fact, the 83-year-old is still hospitalized and was recently diagnosed with cancer.)

Political officials, including Prime Minister Essam Sharaf and senior members of the Muslim Brotherhood, called for calm.