Egyptian security forces have been put on high alert as the North African country marks the fourth anniversary of the revolution that toppled long-time dictator Hosni Mubarak.

On Sunday, Egyptian security officials deployed thousands of troops in major cities across the country.

Egypt security forces have also closed off Cairo's iconic Tahrir Square and halted trains to the city in anticipation of protests.

Media reports say thousands of demonstrators are expected to pour out onto the streets nationwide to commemorate the bloody uprising.

The Muslim Brotherhood and several other opposition groups have called for massive rallies in a bid to revive the revolution.

Social and political activists say the massive rallies are aimed at reviving revolutionary spirit and demanding an end to the military rule that toppled democratically-elected president Mohamed Morsi.

Female Egyptian activist shot dead

The anniversary comes as activists mourn the death of a female protester shot dead Saturday in downtown Cairo while taking part in a gathering commemorating the 2011 uprising.

Activists blame riot police for the death of Shaimaa el-Sabagh, the mother of a five-year-old boy from the Mediterranean port city of Alexandria.

Two policemen injured

On Sunday in Cairo, a bomb wounded two Egyptian policemen who were stationed outside a sports club in the Heliopolis area.

Egypt uprising

The 2011 revolution, which began on January 25, led to the overthrow of Mubarak. In an election after Mubarak’s ouster, Muslim Brotherhood-backed Morsi was elected president.

Morsi was later ousted in a military coup led by former military ruler and current President Abdel Fattah el-Sisi in July 2013.

Egypt clampdown

The Egyptian government has been cracking down on any opposition since Morsi was ousted, and Sisi is accused of leading the suppression of Morsi supporters, as hundreds of them have been killed in clashes with Egyptian security forces over the past year.

Rights groups say the army’s crackdown on the supporters of Morsi has led to the deaths of over 1,400 people and the arrest of 22,000 others, including some 200 people who have been sentenced to death in mass trials.

The UN Human Rights Council has repeatedly expressed concern over the Egyptian security forces’ heavy-handed crackdown and the killing of anti-government protesters.