Tension grips Egypt ahead of Arab Spring anniversary

Egypt is bracing for widespread demonstrations on the third anniversary of the Arab Spring uprising that led to the fall of Hosni Mubarak, a day after a string of bombs killed five people in Cairo. 

Opponents of the current army-backed interim government are expected to hold demonstrations on Saturday, with some calling for the return of the Islamist president, Mohamed Morsi, who became the first elected Egyptian president in 2012 but was removed from power last year in a military intervention backed by popular support.

The military and interim government has since suppressed support of Morsi, killing hundreds of demonstrators and outlawing his organisation, the Muslim Brotherhood.

Backers of the current government have also called for mass rallies.

Security forces have blocked off areas of the capital. Tahrir Square, the epicentre of the popular revolt that toppled Mubarak in 2011, was closed on Saturday ahead of commemorations. 

Mubarak was forced to step down on February 11, 2011 after 18 days of demonstrations in which an estimated 850 people were killed.

The tensions come a day after four bombs killed six people and injured more than 80 in attacks targeting security forces in the capital.

The first blast, at the police's central security directorate building, killed four people and wounded dozens, and left a crater in the ground. It brought down ceilings and damaged exhibits inside the Museum of Islamic Art.

The second blast outside a metro station killed a security officer. The third attacked a police station, while the fourth outside a cinema killed one person.

Ansar Beit al-Maqdis, an al-Qaeda-inspired group led by bedouin fighters in the Sinai Peninsula, said late on Friday that it carried out the attacks to avenge the deaths of Morsi's supporters since his removal.

At least 1,000 people have been killed and thousands of Islamists have been arrested, while the military-installed authorities branded the Brotherhood a  "terrorist" organisation in December following a deadly attack on the police.

The interim government and the pro-Morsi National Pro-Legitimacy Alliance condemned the bombings.

However, the interim interior minister, Mohamed Ibrahim, called for demonstrations in support of the government and to counter what he said was an Islamist "plot to spark chaos".

Ibrahim also vowed security forces would respond with "firmness" to any attempt by the "Muslim Brothers to sabotage the ceremonies".