Egyptian security forces have all but disappeared from the streets in the heart of the country's capital ahead of planned demonstrations against President Hosni Mubarak's rule.
Egyptians had expected a huge police presence ahead of Friday's planned protests.
Instead, there is no sight of riot police on Cairo's main streets and key bridges, including areas where security forces are visible even in normal times.
Before dawn, the largest opposition group, the Muslim Brotherhood, said at least five of its leaders and five former members of parliament had been arrested.
The group's lawyer, Abdel-Moneim Abdel-Maksoud, and spokesman, Walid Shalaby, said a large number of rank and file Brotherhood members have also been detained.