A suicide car bomber struck Cairo police headquarters yesterday, the first of four blasts in Egypt's capital that killed six people on the eve of the anniversary of the 2011 uprising.
The bombings, all targeting the police, came as street clashes between Islamist supporters of deposed president Mohammed Mursi and backers of the military killed seven people, a day before planned rallies to mark the revolt that drove Hosni Mubarak from power.
In the first attack, an assailant rammed a bomb-laden car into a metal fence surrounding the Cairo security directorate at around 6.15am, killing four people and wounding more than 70, police and health ministry officials said.
The bombing damaged the nearby Museum of Islamic Art, bringing down ceilings and damaging a relic wooden prayer niche from the medieval Fatimid period, Culture Minister Mohamed Ibrahim said.
Two other bombs went off hours apart in a neighbourhood close to the Giza pyramids, one killing a person and wounding four conscripts near a cinema.
The other struck outside a police station, without causing any casualties, police said.
"They don't want the people to celebrate [the January 25 anniversary]", Interior Minister Mohamed Ibrahim said of the assailants, adding he expected large crowds to take to the streets following the attacks.
Later, at least seven people were killed when Islamist protesters clashed with their civilian opponents and police in several cities, said security officials state media.
Deadly clashes between supporters and opponents of Mursi have become a weekly ritual since the former president's overthrow. The pro-Mursi National Pro-Legitimacy Alliance condemned the bombing of the security headquarters but said it would go ahead with its "peaceful struggle against (the) coup".
The president's office vowed it would "avenge our martyrs". "Whoever planned, participated, financed, or incited [the attack] will be punished with the worst form of punishment," it said.
A witness to the police headquarters bombing said the booby-trapped car had slammed into the metal fence surrounding the building.
"I was on the third floor, with the head of security," said 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.
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.