CAIRO (AP) ― A car bomb struck the main Egyptian police headquarters Friday in the heart of Cairo, killing at least four people in a hugely symbolic attack on the eve of the third anniversary of the 2011 uprising that toppled longtime autocratic ruler Hosni Mubarak.

The blast shook and damaged nearby buildings, including a nearby museum and courthouse, and sent black smoke rising above the Egyptian capital as a large number of ambulances rushed to the scene.

An Associated Press photographer said about six police officers sat on the sidewalk outside the building and wept. Small parts of a vehicle could be seen scattered around on the road and a corpse ― which officers said was a suicide bomber ― lay under a blanket.

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.

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.

No one immediately claimed responsibility for the 6:30 a.m. blast, but Egypt has seen a sharp rise in Islamic militant attacks targeting police and the military in the aftermath of the July 3 coup that ousted Islamist President Mohammed Morsi. Immediately after the blast, local residents gathered and chanted against Morsi’s Muslim Brotherhood.

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

Interior Ministry spokesman Spokesman Gen. Hani Abdel-Latif said the blast was caused by a car bomb that struck cement blocks placed 5 meters from the outside gates of the building. He declined to comment on earlier reports of subsequent gunfire or that the guards opened fire on suicide car bomber.

The bombing came on the eve of the anniversary of the start of the 18-day mass uprising that toppled Mubarak. It also came hours after a celebration held by the country’s military to honor Police Day.

Egypt plunged in bouts of violence after the July 3 military coup against Morsi and a heavy-handed security crackdown on the Muslim Brotherhood that left hundreds dead and thousands arrested.

A Muslim 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.

Car bombings are common in some areas of Egypt, including the Sinai Peninsula, but they are rare in the capital.

The most prominent attack was 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.

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

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.