Egyptian police arrested dozens of suspected Islamists ahead of planned rallies on Friday as troops beefed up their presence in the capital.
An interior ministry official said 107 alleged members of the blacklisted Muslim Brotherhood were detained on Thursday and Friday on suspicion of planning violent protests after Friday prayers.
The protests have been called by the little-known Salafi Front, part of a group of Islamists who oppose the army's overthrow of president Mohamed Morsi last year.
Morsi's Muslim Brotherhood movement, which has been blacklisted, endorsed the protests without saying whether its harried activists would take part.
Morsi's overthrow unleashed a deadly crackdown on his supporters that killed hundreds of people and saw thousands jailed, including the former president himself.
Police often quickly disperse pro-Morsi protests, which have increasingly given way to bombing attacks in the capital.
The military and police have boosted their presence in the capital and other cities, and warned that they will forcibly disperse any protests.