Egypt's army has warned that anyone on the streets of major cities after curfew at 1600 local time (1400 GMT) will be in danger.
Anti-government protests are now in a fifth day, despite President Mubarak's promise to name a new cabinet.
In Cairo, protesters have clashed with police outside the interior ministry but the army has not yet intervened. Injuries have been reported.
There have also been clashes in the cities of Alexandria and Ismailiya.
Thousands have gathered in the centre of the capital Cairo, where troops and armoured vehicles are deployed but have not yet taken any action against protesters.
Health officials say 38 people have died in clashes across Egypt since Friday.
The latest figures bring the death toll in the week's unrest to at least 45, with both protesters and police officers among the dead. About 2,000 people have been injured.
The Egyptian military has used tanks and armoured personnel carriers to seal off the site of the pyramids on the Giza Plateau, the Associated Press reports.
The army had already secured the Egyptian Museum, home to such treasures as the gold mask of King Tutankhamen, to protect it from looters.
Cairo stock exchange will be closed on Sunday - a full trading day in the Middle East - because of the turmoil in the city.
Friday saw tens of thousands on the streets across Egypt in protests that continued into the night, defying a curfew. In Cairo, protesters set fire to the headquarters of the governing NDP party and surrounded state TV and the foreign ministry.
The powerful Egyptian army, deployed to the streets for the first time since the mid-1980s, is much more respected than the police and many protesters embraced their presence. Whether the 450,000-strong armed forces will remain loyal to Mubarak is key for the nation's future.
