CAIRO - A suicide car bomber struck Cairo police headquarters Friday, 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 Mohamed Morsi 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 about 6:15 am (0415 GMT), killing four people and wounding more than 70, police officials and the health ministry said.The blast, which badly damaged the facade of the building, left a large crater in the ground and sent a plume of smoke billowing above the city, an AFP correspondent reported.Policeman Mahmud Mushref, his head bandaged after being wounded in the blast, said the car had slammed into the metal fence surrounding the building. “I was on the third floor, with the head of security,” said Mushref. “The car crashed into the fence, and the explosion happened.” Interior ministry spokesman Hany Abdel Latif said “the vehicle tried to get close to the building but was stopped at the gate. Casualties were relatively small given the size of the blast.”Friday is the Muslim day of prayer and rest, and so relatively few people were on the streets. The bombing also damaged the nearby Museum of Islamic Art, bringing down ceilings and damaging exhibits, culture minister Mohamed Ibrahim told AFP.State television said investigators had found the remains of the suspected suicide bomber. Hours later, a small makeshift bomb exploded near a police vehicle close to a metro station in the neighbourhood of Dokki, killing a police conscript, security officials 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, the interior minister, who is also named Mohamed Ibrahim, said of the assailants. The president’s office vowed to “avenge our martyrs”. “Whoever planned, participated, financed, or incited (the attack) will be punished with the worst form of punishment,” it said. 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 Morsi supporters and Islamists have become a weekly ritual since the former president’s overthrow. The pro-Morsi National Pro-Legitimacy Alliance condemned the bombing of the security headquarters but said it would go ahead with its “peaceful struggle against (the) coup”. A witness who lives in an apartment about 200 metres (yards) away from the police building said he had been awakened by the explosion. “My building shook,” Yahya Attiya said.Riot police pushed back hundreds of onlookers, some of whom chanted slogans against Morsi’s Muslim Brotherhood.Militants have escalated attacks since the military overthrew Morsi on July 3 after only a year of turbulent rule.The Brotherhood has denied involvement in those 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, but many blame the Brotherhood.“I can now call the Muslim Brotherhood the terrorist Brotherhood,” said Attiya, as he surveyed the wreckage outside the police headquarters.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.