Violence has broken out between supporters and opponents of President Mohamed Morsi in Egypt's second city of Alexandria as rival rallies were held throughout the country.
Two people were killed when protesters stormed an office of Egypt's ruling Muslim Brotherhood in the city's Sidi Gaber neighbourhood, Reuters reports.
The Muslim Brotherhood said eight of its offices had been attacked on Friday, including the one in Alexandria.
Officials said more than 70 people had been injured in the clashes in the city. One person was shot dead and a young American man who was using a small camera died after being stabbed in the chest.
In Cairo, thousands of Islamists gathered round a mosque after weekly prayers to show support for the president.
Some opposition gatherings were also under way. A handful of protesters watched security men ringing the presidential palace, the focus for Sunday's Cairo rally. Mursi has moved elsewhere.
A few thousand milled around in the capital's Tahrir Square, cradle of the revolution. Some waved red cards reading "Out!", in preparation for the big demonstration against the president.
The army, which heeded mass protests in early 2011 to push aside Mubarak, has warned it will intervene again if there is violence and to defend the "will of the people". Both sides believe that means the military may support their positions.
US warns against Egypt travel
The US has warned Americans not to travel to Egypt and has told non-emergency diplomatic staff to leave, as clashes continued in the country.
The BBC reports that the state department also urged US nationals in Egypt "to remain alert".
Tensions have been rising ahead of a mass rally planned by the opposition on Sunday, calling Mr Morsi to step down.
His supporters are stressing what they see as Mr Morsi's "legitimacy", rejecting the opposition's demand.
Sunday is the first anniversary of the president's inauguration.
In a warning on Friday, the state department said it had "authorised the departure of a limited number of non-emergency employees and family members" from Egypt.
It asked Americans "to defer non-essential travel to Egypt at this time due to the continuing possibility of political and social unrest".
Cairo's main airport was packed with departing passengers, and all flights leaving for Europe, the US and the Gulf were fully booked, officials were quoted as saying.