Five people, including an Egyptian female journalist, were killed in Cairo as police clashed with protesters demonstrating against ex-army chief Abdel Fattah el-Sisi's presidency bid, a security official said.
The violence erupted as supporters of deposed President Mohamed Morsi took to the streets of Cairo, Alexandria and other cities on Friday to vent their anger at Sisi, who overthrew the Islamist nine months ago.
Mayada Ashraf, 23, who worked for the privately owned Al-Dustour newspaper, was shot in the head while covering clashes in the northern neighbourhood of Ein Shams, the official said. A further three people were killed in the same violence.
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Four people were wounded in clashes in the northern province of Damietta, health ministry official Khaled al-Khatib told AFP news agency.
In Cairo's eastern neighbourhood of Madinat Nasr, students from Al-Azhar Islamic university hurled petrol bombs and stones at riot police who fired tear gas to disperse them, security officials said.
Underlining Egypt's deep polarisation, clashes also erupted between Morsi supporters and his opponents in the northern Cairo districts of Ein Shams and Matareya, the officials said.
Ten Morsi supporters were arrested in clashes with security forces in Damietta province, and 28 were arrested in the southern Minya province for carrying leaflets hostile to the military and the police, they added.
Demonstrators in the southern Cairo working class district of Helwan and in Fayum province, southwest of the capital, fired birdshot and police responded with tear gas, state news agency MENA reported.
Supporters of the widely popular presidential hopeful, who toppled Morsi after massive street protests against his turbulent one-year rule, also demonstrated to celebrate his candidacy.
Carrying Egyptian flags and portraits of Sisi, dozens marched in Alexandria and scores gathered in Cairo's iconic Tahrir Square, symbol of the 2011 uprising that toppled veteran President Hosni Mubarak.
Sisi, who was also defence minister and deputy prime minister, announced his resignation on Wednesday to enable him to stand in the election.
His candidacy is likely to further inflame Islamist protesters and worry secular activists who fear a return to rule by the military and the strong-arm tactics of the Mubarak era.
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.