Five people have been killed in three separate bomb attacks in Greater Cairo on Friday morning.
A large blast ripped through a security building in central Cairo early on Friday, killing four and injuring 76 others, according to the health ministry.
The explosion at the Cairo Security Directorate in Bab El-Khalk district blew out the windows of the building and stripped off parts of its façade, state TV reported.
According to a statement by the interior ministry, a car packed with explosives was passing in front of the directorate and stopped suddenly in front of the gate before exploding. The attack took place at around 6:30am local time and was heard across several parts of the capital.
TV footage showed wrecked floors of the multi-storey building and a damaged facade of the nearby Museum of Islamic Art. The minister of state for antiquities told journalists in a statement after touring the site that "some artefacts" inside the museum had also been damaged.
Police have cordoned off the area and ambulances rushed to the scene to transport the wounded
Large crowds of onlookers chanted slogans against the Muslim Brotherhood movement of deposed president Mohamed Morsi, including: "the people want the execution of the Brotherhood. Execution for Morsi." The Brotherhood was designated a terrorist organisation by the cabinet in December.
An Ahram Online reporter at the scene an hour after the blast said she saw a badly mangled vehicle stained with blood parked in front of the police compound. Some of the building's walls have collapsed.
The attack has also caused water pipes in the area to explode, and vacuum excavators were sent to remove the water pooling in the street, the reporter added.
Later on, one person was killed when a primitive bomb exploded after being thrown at a police vehicle near a metro station in Giza, deputy Giza security chief Mahmoud Farouk told state TV.
TV footage showed a police cordon around El-Behous metro station in Giza's Dokki district.
At least 11 others were reportedly wounded in the attack.
A third bomb also exploded later on Friday morning at a police station in Talbiya district in Giza. The interior ministry said the bomb was small and had caused no casualties.
"It's a vile, desperate attempt by evil terrorist forces to disrupt the success Egypt and its people have achieved in the [transitional] roadmap and the passing of the new constitution," Prime Minister Hazem El-Beblawi commented, in reference to the Cairo bomb.
The attacks came only one day ahead of the third anniversary of the 2011 uprising that toppled president Hosni Mubarak, raising the spectre of further violence.
"They don't want the people to celebrate," interior minister Mohamed Ibrahim told reporters while inspecting the explosion site in Cairo, adding that he was certain that "millions would take to the streets" on Saturday to celebrate the revolution nonetheless. He added that the "despicable attack" would not hamper police "in their war against black terrorism."
A spate of recent explosions in densely populated areas has raised fears that militant activity in the border Sinai Peninsula, which has spiked since Morsi's removal, would take its toll on other parts of the country.
But the Brotherhood has repeatedly denied any links to the attacks.
In one of the deadliest attacks, a December bombing of a security headquarters the Nile Delta city of Mansoura killed 16 people, mostly policemen.
A bomb also exploded outside a Cairo court just before polls were to set to open in last week's constitutional referendum, leaving no casualties.
An Al-Qaeda-inspired group, Ansar Beit Al-Maqdis, has claimed responsibility for most of the recent attacks in which scores of policemen and soldiers were killed. The group says the violence is in revenge for the killings and arrests of Islamists as part of a broad security crackdown. But there was no immediate claim of responsibility for Friday's attack.
The group also claimed a failed assassination attempt on the interior minister in Cairo in September.