A bomb blast wounded a policeman in Cairo on Sunday, the interior ministry said, as Egypt tightened security on the fourth anniversary of the 2011 uprising that ousted ex-President Hosni Mubarak.

A bomb blast wounded a policeman in Cairo on Sunday, the interior ministry said, as Egypt tightened security on the fourth anniversary of the 2011 uprising that ousted ex-President Hosni Mubarak.

Armored vehicles were stationed around Cairo's iconic Tahrir Square -- the epicenter of the revolt against Mubarak -- after Muslim Brotherhood called for protests on Sunday against President Abdel Fattah al-Sisi.

Former army chief Sisi toppled Mubarak's successor Mohammad Mursi in July 2013 and has since led a crackdown on Mursi supporters that has left hundreds dead.

Militants have regularly targeted security forces since Mursi's ouster, killing scores of policemen and soldiers.

The interior ministry said Sunday's bomb exploded in eastern Cairo's Alf Maskan neighborhood, where a similar blast on Friday claimed by armed group Ajnad Misr (Troops of Egypt) wounded four policemen and a civilian.

It provided no further details on the blast or the condition of the wounded police officer.

Tensions have been running high ahead of Sunday's anniversary and a female demonstrator was killed in clashes with police during a rare leftwing protest in central Cairo on Saturday.

An 18-year-old female protester was also killed on Friday in clashes in the Mediterranean city of Alexandria.

Police have warned they would "decisively" confront protests on Sunday.

Mursi's supporters often hold small rallies that police quickly disperse.

The revolt against Mubarak erupted on January 25, 2011, with hundreds of thousands of protesters taking to the streets across Egypt for 18 days until he stepped down.

The anti-Mubarak revolt was fuelled by police abuses and the corruption of the his three-decade rule, but the police have since regained popularity amid widespread yearning for stability.