Three bombings hit high-profile areas around Cairo on Friday, including a suicide car bomber who struck the city's police headquarters, killing five people in the first major attack on the Egyptian capital as insurgents step up a campaign of violence following the ouster of the Islamist president.

Nobody claimed responsibility for the attacks, but they bore the hallmarks of Islamic extremists who have increasingly targeted police and the military since the July 3 coup against Mohammed Morsi and a fierce crackdown on his supporters led by the Muslim Brotherhood.

The explosions struck as the country was on high alert ahead of the third anniversary of the January 25 start of the 2011 uprising that toppled autocratic leader Hosni Mubarak. Morsi's supporters had vowed to use the event to gain momentum in their efforts turn to a new momentum to "break the coup."

Friday's violence began when a suicide bomber rammed a car into cement blocks surrounding the main Egyptian police headquarters in the heart of Cairo, killing at least four people and sending billows of black smoke into the sky. The blast also tore through nearby buildings, including the renowned Museum of Islamic Art.

Egypt's antiquities minister, Mohammed Ibrahim, said the explosion badly damaged the facade of the 19th century museum and artifacts inside, including a rare collection of Islamic art objects dating back to 1881. He said the museum, which was recently renovated in a multimillion dollar project, will have to be "rebuilt."

As a large number of ambulances rushed to the scene, an Associated Press photographer saw about six police officers weeping as they on the sidewalk outside the building. Small parts of a vehicle were scattered on the road and a blanket covered a corpse — which officers said was the suicide bomber.

Several floors of the high-rise security building were wrecked, air conditioning units dangled from broken windows, and the pavement outside was covered with piles of shattered glass, pieces of bricks and rocks. The facade of the adjacent Islamic Art Museum and a court house were also damaged along with shops and cars in the area.

Egypt's Interior Minister Mohammed Ibrahim described the attack "vile terrorist act" and vowed, "it will not discourage the police from continuing their fierce war against the black terrorism."

The Interior Ministry cordoned off the building, which is located in a busy district, as rescue teams worked to extract victims trapped in the rubble. Security forces went on high alert, and closed the central Tahrir Square and main roads, including the one leading to the Interior Ministry.

The Health Ministry said in a statement that four people were killed and nearly 50 wounded.

About two hours later, another bomb struck a police car on patrol near a metro station near the Russian Culture Center elsewhere in Cairo, killing one person and wounding eight others, officials said.

A third, smaller blast targeted the Talbiya police station about four kilometers (two miles) from the famous Giza Pyramids but caused no casualties, officials said.

The officials spoke on condition of anonymity because they were not authorized to speak to the media.

The attacks came a day after the country's military and security leaders marked Police Day depicting security forces as national heroes battling terrorism.

The military-backed government has blamed the Brotherhood for past attacks and designated it as a terrorist organization. The group has denied the accusations as baseless.

The most prominent attacks were a failed assassination attempt on the interior minister in Cairo in September and the December suicide car bombing that targeted a security headquarters in the Nile Delta city of Mansoura, leaving nearly 16 dead, most of them policemen.

An Al-Qaida-inspired group called Ansar Beit al-Maqdis, or the Champions of Jerusalem, has claimed responsibility for most of the recent attacks, saying they aimed to avenge the killings of Morsi's supporters in the months-long heavy security crackdown on protesters demanding his reinstatement and denouncing the coup.

A Brotherhood-led coalition had planned protests after Friday prayers across the country as part of their near-daily demonstrations against Morsi's overthrow and the recent vote on the country's rewritten constitution.

Open gallery view Cairo Security Directorate after a bomb attack, January 24, 2014. Credit: Reuters