Egyptian police have used tear gas to disperse small demonstrations in Cairo by supporters of ousted president Mohamed Morsi on the second anniversary of the killing of hundreds of protesters by security forces.
Police were deployed at the capital's main intersections and outside government buildings on Friday.
They fired tear gas at three rallies in which dozens of demonstrators took part in western Cairo, police officials said.
In the north of the capital, tear gas was also used against Morsi supporters hurling large firecrackers, they said.
The Rabaa al-Adawiya killings of August 14, 2013, when police shot dead hundreds of Morsi supporters as they dispersed a protest camp, has remained a rallying point for Egypt's Islamist opposition. While the exact death toll is not known, estimates range from 700 to 1,000.
Two years on, no policemen have faced trial over the incident.
'Crimes against humanity'
The Egyptian government-appointed National Council for Human Rights reported last year that the violence at Rabaa began after armed protesters shot and killed a policeman.
But rights groups have said 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 called on Friday on the United Nations Human Rights Council to launch an inquiry into the killings.
OPINION: Rabaa's massacre - The political impact
Based on interviews with more than 200 witnesses, Human Rights Watch stated that only a few protesters were armed at Rabaa; they fired on security forces in "at least a few instances", and threw rocks and Molotov cocktails only after the break-up of the protest began.
The group said that Egyptian security forces, meanwhile, fired on makeshift medical facilities, and "positioned snipers to target whoever sought to enter or exit" the Rabaa hospital.
Solidarity events were held outside Egypt on Friday.
In London, activists staged what they called a "die-in" protest - not only to raise awareness of the massacre, but also to demonstrate their opposition to a possible visit by President Abdel Fattah el-Sisi, the former military leader accused by many of being responsible for the killings.
Morsi, the country's first democratically elected leader, ruled for only a year before the military overthrew and detained him following mass protests against his rule. He has since been sentenced to death.
Sisi has pledged to eradicate Morsi's Muslim Brotherhood. The group has been blacklisted and most of its leaders arrested, severely restricting its ability to mobilise supporters to take part in protests.