Egyptian police have fired tear gas to disperse anti-government protesters who gathered for counter-rallies on Saturday, as the government holds ceremonies to mark the third anniversary of the uprising that toppled Hosni Mubarak. Reports said at least four protesters were killed.
The protesters include backers of former Islamist president Mohamed Morsi and opponents of the current military-installed government.
Their demonstrations in Cairo are taking place as government supporters gather at other locations in the capital to commemorate Egypt's 2011 Arab Spring uprising.
A bomb exploded outside a Cairo police academy before Saturday's rival rallies got underway. There are also reports of a second bombing in a different part of the city.
The incident comes a day after six police officers were killed in a series of explosions that rocked Cairo.
Ansar Beit al-Maqdis, which ideologically opposes the Muslim Brotherhood, released a statement Saturday claiming responsibility. The statement also warned Muslims to stay away from police stations. The group has also claimed responsibility for a September 2013 bombing in Mansoura and other attacks, saying they were carried out to avenge the military-backed government's crackdown on Islamists.
At least 20 people died Friday across Egypt, including six policemen. Authorities say the remaining deaths occurred in clashes among Islamist protesters, their secular opponents and police.
The 2011 Arab Spring uprising that swept through large parts of the Middle East raised hopes in Egypt for a stable democracy in the Arab world's largest nation. Instead, the country has been mired in political turmoil, as Morsi backers battle to regain control of the country from the military-backed government that drove him from power in a July army takeover.
Morsi came to power as Egypt's first democratically elected president after Hosni Mubarak stepped down under pressure nearly three years ago.
Just more than two years later, the military-installed government of secularists and liberals that replaced Morsi designated the Muslim Brotherhood a terrorist group following a bombing of security offices in the Nile Delta city of Mansoura that killed 15 people.
Ansar Beit al-Maqdis, which derides the Brotherhood for lack of militancy, claiming responsibility for the Mansoura bombing.