At least five people were killed Friday and 88 others were wounded, including three law-enforcement officers, in three explosions targeting police in different parts of the Egyptian capital, security sources told Efe.

In the deadliest attack, a car-bomb blast shortly before 7:00 a.m. outside the main Egyptian police headquarters in Cairo left four dead and 73 wounded.

The explosion severely damaged the facade of the headquarters; it also seriously damaged other nearby buildings, including a courthouse and the Museum of Islamic Art, the Interior Ministry said in a statement.

"It's an attack that shouldn't have happened in Egypt. It's the work of the Muslim Brotherhood, but they need to know we'll never surrender. As much harm as they do to us, we'll fight back even more," Ahmed Abdelaziz, a 48-year-old resident of the downtown area where the bomb blast occurred, said.

Another explosion just over two hours later killed a police officer and wounded 15 others near a metro station in the capital's Dokki neighborhood.

Most of the injured were passengers of a minibus, the ministry said.

Finally, there were no reports of casualties in a third attack on a police station in Talbeya, a neighborhood on Cairo's outskirts.

The bombings came on the eve of the third anniversary of the start of the 2011 uprising that ousted strongman Hosni Mubarak.

The Interior Ministry said in a statement that they were "terrorist and cowardly" and an attempt to prevent Egypt from celebrating that anniversary.

Attacks targeting Egypt's security forces have been on the rise since the ouster of Islamist President Mohammed Morsi in a July coup and the subsequent crackdown on his Muslim Brotherhood movement.

On Thursday, at least five police officers were killed, including three sergeants, and two others were wounded in an armed attack on a security checkpoint south of Cairo in the Egyptian province of Beni Suef.

The Brotherhood and allied groups have held demonstrations at universities across Egypt since Morsi was deposed by the armed forces in the July 3 putsch, which followed days of massive anti-government protests.

Morsi is on trial for inciting the murder of his opponents and also faces other charges including treason that are punishable by execution.

While in office from June 2012 to July 2013, Morsi and the Brotherhood were accused by critics of doing little to address poverty and Egypt's struggling economy, of failing to advance the goals of the 2011 revolution that forced out Mubarak and of seeking to monopolize power. EFE