A bomb blast wounded at least one Cairo policeman on Sunday, just days after two female protestors were killed amid tightened security across Egypt on the fourth anniversary of the uprising that ousted autocrat Hosni Mubarak.

According to reports from news agency AFP, the blast targeted police stationed in Cairo's Alf Maskan district where a similar explosion occured on Friday. The blast, claimed by a jihadist group, wounded four policemen and one civilian.

In another part of Cairo, activists gathered to commemorate the death of Shaimaa el-Sabagh, a 34-year-old mother who was shot dead during a rare leftist protest on Saturday as tensions ran high ahead of Sunday's anniversary. Videos posted online show el-Sabagh amongst demonstrators chanting and laying wreaths to commemorate the more than 900 protestors who died in the 2011 uprising. Gunfire, allegedly by police firing birdshot at the crowd, can then be heard before a bloodied el-Sabagh is carried away.

Only the day before, an 18-year-old woman was killed while protesting in the Mediterranean city of Alexandria. At another rally there on Sunday, this time organized by Islamists, a third protester lost his life after allegedly shooting first at police.

Leftists and Islamists barred from demonstrating

Security forces under President Abdel-Fattah el-Sissi have clamped down hard on demonstrations. Twenty-two armored vehicles surrounded Cairo's famed Tahrir Square on Sunday, the heart of the revolt which ended Mubarak's three-decade rule. Security was also beefed up at other key points around the city after an Islamist coalition opposed to el-Sissi announced its intentions to stage street protests to mark the anniversary.

Islamists and supporters of former President Mohammed Morsi, of the now-outlawed Muslim Brotherhood have faced a similar crackdown. Thousands of Muslim Brotherhood members have been imprisoned or are awaiting trial.

In a televised address on Saturday, Sissi acknowledged Egyptians' frustrations but called on citizens to exercise patience, as it would take time to achieve "all of the revolution's goals."

es/jlw (AP, AFP, Reuters)