Deadly strike: A police officer orders people back from the scene of the car bomb attack on police headquarters in Cairo on Friday.

Deadly strike: A police officer orders people back from the scene of the car bomb attack on police headquarters in Cairo on Friday. Photo: AP

Cairo: A string of four bombings hit around Cairo on Friday, including a car blast that ripped through the Egyptian capital's main security headquarters and wrecked a nearby museum of Islamic artefacts.

Six people were killed in the most significant attack yet in the city at a time of mounting confrontation between Islamists and the military-backed government.

The attacks fuelled fears of an increasing militant insurgency in retaliation for the military's July 3 ouster of Islamist President Mohammed Mursi and the subsequent crackdown on his Muslim Brotherhood and other Islamists.

The first bomb struck the Cairo security directorate about 6.15am on Friday, killing at least four people and wounding 76, the Health Ministry said.

Outcry: A man holds a poster of army chief General Abdel Fatah al-Sisi during an anti-Muslim Brotherhood protest after the explosions.

Outcry: A man holds a poster of army chief General Abdel Fatah al-Sisi during an anti-Muslim Brotherhood protest after the explosions. Photo: Reuters

Hours later, a small makeshift bomb was set off near a metro station, followed by a bomb outside a police station on a road leading to the Giza pyramids.

The hours after the bombings saw a public backlash against the Brotherhood, which the government accuses of being behind the months-long wave of bombings and shootings, though it denies any link.

Angry residents joined in with security forces in clashes with Brotherhood supporters holding their daily protests in several districts of the capital and multiple cities across the country in violence that left eight dead.

In one Cairo neighbourhood, pro-Mursi protesters clashing with security forces set fire to a police kiosk, sending a pall of smoke in the air.

As police drove back from clashes with Brotherhood supporters in the capital's Giza district in the afternoon, they were hit by the day's fourth bombing — a roadside explosive that killed one policeman and wounded four others on Haram Street, a main avenue leading to the famed Giza Pyramids.

The attacks occurred 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.

An officer who saw the police headquarters bombing said the booby-trapped car had stopped at the metal fence surrounding the building before the bomb exploded.

"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."

The explosion left a large crater in the ground and sent a plume of smoke billowing above the city.

"Casualties were relatively small given the size of the blast," Interior Ministry spokesman Hany Abdel Latif said.

Yahya Attiya, a witness who lives in an apartment about 200 metres from the police building, said he the explosion woke him.

"My building shook," he said.

Hours later, the small bomb set off near a central Cairo metro station wounded five police officers, the Health Ministry said.

State television reported one person was killed in the blast, but that was not immediately possible to confirm.

The facade of police headquarters and the front of the nearby Museum of Islamic Art were badly damaged by the earlier blast.

The Interior Ministry said the bomb was detonated by the high metal fence surrounding the police building.

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.

Dr 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 on Friday to mark the January 25 anniversary of the 2011 uprising against Mr Mubarak, accusing the military-backed government of continuing autocratic rule.

The country has been deeply divided since Dr Morsi's overthrow, between his Islamist supporters and backers of the military, which accuses the Brotherhood of terrorism.

The Brotherhood has condemned previous attacks against the police and army since Dr Morsi's overthrow.

Scores of soldiers and police have been killed on the Sinai Peninsula, and militants in the desert region have begun to expand their operations to densely populated areas of the rest of the country.

AFP, AP