Police clashed Friday with Islamists protesting against a decision by ex-army chief Abdel Fattah al-Sisi to stand for president, state media said, underlining Egypt's deep polarisation.
Supporters of deposed president Mohamed Morsi took to the streets in Cairo, Alexandria and other Egyptian cities to vent their anger at Sisi who overthrew the Islamist leader nine months ago.
Demonstrators in the southern Cairo working class district of Helwan and in Fayum, southwest of the capital, fired birdshot and police responded with tear gas, state news agency MENA said.
The protesters also cut off roads in Helwan, in the western Cairo neighbourhood of Giza and in Madinat Nasr further east, the agency said.
Police likewise fired tear gas at demonstrators in the Mediterranean city of Alexandria, Egypt's second city, MENA said.
In Fayum, clashes erupted between Morsi supporters and opponents of the Islamist leader, with security forces intervening to stop the fighting, MENA said, without giving details.
It said dozens of Morsi supporters linked arms and formed a human chain spanning several kilometres (miles) in the northern province of Beheira.
Opponents of Sisi also torched a huge portrait of the former army chief in the Suez canal city of Port Said, MENA said.
Supporter of the widely-popular presidential hopeful, who toppled Morsi after massive streets protests against his turbulent one-year rule, were also out on the street to celebrate his candidacy.
Dozens took to the streets in Alexandria while scores gathered in Cairo's iconic Tahrir Square, symbol of the 2011 uprising that toppled veteran president Hosni Mubarak.
Sisi faces no serious competition in his bid for the presidency and is widely seen as the only leader able to restore order after more than three years of turmoil since the Arab Spring uprising.
His candidacy is likely to further inflame Islamist protests and worry secular activists who fear a return to rule by the military and the strong-arm tactics of the Mubarak era.
Morsi's Muslim Brotherhood rejected Sisi's candidacy outright and a coalition of his supporters had called for Friday's protests.
"What we said nine months ago was confirmed and the mask fell off from the face of the coup leader... with the announcement of his candidacy to 'the bloody presidency'", a statement said Thursday.
Sisi "broke the oath he made before the elected president Mohamed Morsi by toppling him and made the Egyptian army enter the political arena with him," the coalition added.
Since Morsi's ouster, his supporters have been staging weekly protests calling for his reinstatement.
Their rallies have often descended into deadly street clashes with security forces and civilian opponents. Their numbers have sharply decreased amid a violent security crackdown.
More than 1,400 people have been killed in the crackdown, according to Amnesty International, and thousands have been jailed.