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Verdicts for the remaining 52 defendants, including nine security officials, are to be delivered March 9. Some have been charged with murder, and others with assisting the attackers. All the defendants — who were not present in the courtroom Saturday for security reasons — can appeal the verdict.

In Port Said on Sunday, army troops backed by armored vehicles staked out positions at key government facilities to protect state interests and try to restore order.

The military issued a statement urging Port Said residents to exercise restraint and protect public property, but also it warning that troops would deal “firmly” with anyone who “terrorizes” citizens or infringes upon the nation’s security and stability.

Rioters on Saturday attacked the prison where the defendants were being held and tried to storm police stations and government offices around the city. Health officials say at least 37 people were killed, including two policemen, in the rioting on Saturday.

The clashes in Port Said were the latest in a bout of unrest across the country that has left 48 people dead since Friday. That death toll includes 11 people killed in clashes between police and protesters marking the second anniversary of the uprising that overthrew Mr. Mubarak after nearly 30 years of authoritarian rule.

Clashes broke out in Cairo for the fourth straight day on Sunday, with protesters and police near central Tahrir Square, birthplace of the 2011 uprising. Police fired tear gas while protesters pelted them with rocks.

The clashes show how turmoil was deepening in Egypt nearly seven months after Mr. Morsi took office. Critics say he has failed to carry out promised reforms of the judiciary and police, and they claim little has improved in the two years since the uprising.

At the heart of the rising opposition toward Mr. Morsi’s government is a newly adopted constitution, which was ratified in a nationwide referendum.

Opponents claim the document has an Islamist slant. It was drafted hurriedly by the president’s allies without the participation of representatives of liberals and minority Christians on the panel that wrote the charter.

Protesters on the streets this past week demanded the formation of a national unity government, early presidential elections and amendments to disputed clauses in the constitution.

Mr. Morsi and the Muslim Brotherhood, the Islamist group from which he hails, counter that the opposition was seeking to overturn the results of democratic and free elections. The Brotherhood, a well-organized and established political group in Egypt for decades, has emerged as by far the most powerful force in post-Mubarak Egypt.

As the situation in Port Said spiraled out of control Saturday, police disappeared from the city’s streets, residents and security officials said, staying put in their camps, police stations and the city’s security headquarters.

The military then dispatched troops to the city, taking up positions at vital state facilities, including the local power and water stations, the city’s main courthouse, the local government building and the city prison. Navy sailors were guarding the local offices of the Suez Canal company.

Navy vessels were escorting merchant ships sailing through the international waterway, a vital income earner for Egypt’s beleaguered economy. Military helicopters were flying over the canal to ensure the safety of shipping, according to Suez Canal spokesman Tareq Hassanein.

Residents said Port Said was quiet overnight except for intermittent bursts of gunfire. The city was still on edge early Sunday — but streets were largely deserted, stores were closed for the second successive day, and some hotels asked guests to leave, fearing more violence.