Egyptian police bolstered their presence in the capital on Friday in anticipation of protests on the second anniversary of the mass killing of Islamist demonstrators in which hundreds died.
The Rabaa al-Adawiya killings, when police shot dead at least 700 supporters of ousted Islamist president Mohamed Morsi as they dispersed a protest camp, has remained a rallying point for the country's harried Islamist opposition.
Police officials said they were deploying in main streets and government buildings amid calls for protests to remember the event, one of deadliest of the Arab Spring period.
Two years later, no policemen have faced trial over the incident, but leaders and members of Morsi's Muslim Brotherhood have.
About 10 police were killed during the dispersal, after coming under fire from several gunmen in the sprawling camp on a crossroads in eastern Cairo when they moved to break it up.
But rights groups have said that police used disproportionate force, killing many unarmed protesters in what Human Rights Watch said "probably amounted to crimes against humanity."
The New York-based group on Friday called on the United Nations Human Rights Council to launch an inquiry into the killings.
"Washington and Europe have gone back to business with a government that celebrates rather than investigates what may have been the worst single-day killing of protesters in modern history," deputy Middle East director Joe Stork said.
"The UN Human Rights Council, which has not yet addressed Egypt's dangerous and deteriorating human rights situation, is one of the few remaining routes to accountability for this brutal massacre."
In Egypt however, the government has always defended the dispersal, insisting that the Islamists were armed "terrorists".
Morsi, the country's first democratically elected leader, ruled for only a year before mass protests prompted the military to overthrow and detain him. He has since been sentenced to death.
President Abdel Fattah al-Sisi, the former leader of the army, had pledged to eradicate Morsi's Muslim Brotherhood.
The group has been blacklisted and most of its leaders arrested, severely restricting its ability to mobilise followers in protests.