Cairo - Three bombs hours apart hit Cairo police headquarters and policemen in the Egyptian capital on Friday killing at least five people on the eve of the anniversary of the 2011 uprising against Hosni Mubarak.
The first bomb struck the Cairo security directorate around 6.15am (04.15 GMT), killing four people and wounding more than 70, the health ministry said.
Hours later, another bomb, a small makeshift device, was set off near a police vehicle close to a metro station, killing one person, according to the health ministry. That was followed by a third outside a police station on a road leading to the Giza pyramids.
The attacks came a day before police were to deploy across the capital for the third anniversary of the uprising against Mubarak, with Islamists calling for mass protests against the new regime.
"They don't want the people to to celebrate," the January 25 anniversary, interior minister Mohamed Ibrahim said of the assailants, adding he expected large crowds to take to the streets on Friday.
A witness to the police headquarters bombing said the booby trapped car had stopped at the metal fence surrounding the building before the bomb went off.
"I was on the third floor, with the head of security," said the policeman, Mahmud Mushref, his head bandaged after he was injured in the blast.
"The car crashed into the fence, and the explosion happened," he said.
The blast left a large crater in the ground and sent a plume of smoke billowing above the city, an AFP correspondent reported.
"Casualties were relatively small given the size of the blast," said interior ministry spokesman Hany Abdel Latif.
Friday is the Muslim day of prayer and rest and so relatively few people were on the streets.
A witness who lives in an apartment about 200 metres away from the police building said he had been woken up by the explosion.
"My building shook," Yahya Attiya said.
Hours later, the makeshift bomb went off near a central Cairo metro station, killing one person, the health ministry said.
Ibrahim, the interior minister, said the bomb targeted a vehicle transporting policemen to their base.
The third small bomb was placed behind a billboard near a police station on the road leading to the Giza pyramids, the interior ministry said, adding it caused no casualties.
The facade of police headquarters and the front of the nearby Museum of Islamic Art were badly damaged by the earlier blast.
Riot police pushed back hundreds of onlookers, some of whom chanted slogans against the Muslim Brotherhood.
Militants have escalated attacks since the military overthrew Islamist president Mohamed Morsi in July.
Morsi's Muslim Brotherhood has denied involvement in the attacks, but was blacklisted as a terrorist group after 15 people were killed when a suicide bomber blew up a vehicle at a police headquarters north of Cairo in December.
An Al-Qaeda inspired group, Ansar Beit al-Maqdis, claimed responsibility for that attack.
The Brotherhood has called for protests starting Friday to mark the January 25 anniversary of the 2011 uprising against Mubarak, accusing the military-backed government of continuing autocratic rule.
The country has been deeply divided since Morsi's overthrow, between his Islamist supporters and backers of the military which accuses the Brotherhood of terrorism.
"I can now call the Muslim Brotherhood the terrorist Brotherhood," said Attiya, as he looked at the wreckage outside the police headquarters.
"They should all be executed," he said.
Others in the crowd near the bomb site carried Egyptian flags and some held up posters of army chief Abdel Fattah al-Sisi, the general who overthrew Morsi.
The Brotherhood has condemned previous attacks against the police and army since Morsi's overthrow.
Scores of soldiers and police have been killed in the restive Sinai Peninsula and militants in the desert region have begun to expand their operations to densely populated areas of the rest of the country.
On Thursday, masked assailants on motorbikes gunned down five policemen at a checkpoint south of Cairo.
There have also been several bombings in Cairo, including a failed assassination attempt against the interior minister in September, weeks after policemen killed hundreds of Islamist demonstrators in clashes at a protest camp.
More than 1,000 people, mostly Islamists, have been killed in street clashes since Morsi's overthrow.
Thousands more have been jailed, including the ousted president and other Brotherhood leaders.