CAIRO -- A string of bombings hit police around Cairo on Friday, including a car blast that ripped through the city's main police headquarters and wrecked a nearby museum of Islamic artifacts. Five people were killed in the most significant attack yet in the Egyptian capital at a time of mounting confrontation between Islamists and the military-backed government.
The blasts further hike tensions a day before rival rallies planned by both military supporters and their Islamist opponents on the third anniversary of Egypt's 2011 uprising that toppled autocrat Hosni Mubarak.
There was no immediate claim of responsibility. But the bombings fueled the government's campaign to paint its top political opponent, the Muslim Brotherhood, as behind a wave of militant violence that has escalated since the military's July 3 ouster of Islamist President Mohammed Morsi and the subsequent crackdown on the Brotherhood.
Soon after the blast at the security headquarters, a crowd gathered outside the building, chanting slogans against the Brotherhood and in support of army chief Gen. Abdel-Fattah el-Sissi, the man who ousted Morsi and who military supporters now want to run for president.
"Execution for Morsi and his leaders," one man shouted through a megaphone. A woman held up a picture depicting the Brotherhood as sheep, screaming, "Morsi is the butcher and el-Sissi will slaughter him."
Later in the day, anti-Islamist residents joined police in clashes with Brotherhood members holding their daily protests in multiple cities around the country. The clashes left at least three protesters dead. Elsewhere, there were several pro-military rallies in the streets, and TV networks aired phone calls from listeners calling on el-Sissi to deal a decisive blow to the Brotherhood.
Islamic militants have increasingly targeted police and the military with bombings and shootings. A day earlier, an al-Qaida-inspired group that claimed previous attacks released an audio message warning police and soldiers they will be targeted in a wave of violence unless they defect.
But authorities have accused the Brotherhood as being behind the violence, branding it officially as a terrorist organization. The Brotherhood has called the accusation baseless. But the branding has helped fuel a wave of popular sentiment against the group and in favor of the military. Security forces have painted their crackdown on Morsi's backers as part of the fight against terrorism, arresting thousands of its members.
Interior Minister Mohammed Ibrahim, who is in charge of police, called the bombings a "vile terrorist act" aimed at spreading panic ahead of Saturday's pro-military rallies. He implicitly blamed the Brotherhood, without naming it, saying, "They will reach a point where coexistence will be impossible."
"But people will only increasingly insist ... and join the masses in millions" on Saturday, he told reporters outside the bombed police headquarters.
The office of interim President Adly Mansour vowed in a statement after the attack that it is determined to "uproot terrorism" and said it could be forced to take "exceptional measures." It did not elaborate.
In a statement, the Brotherhood condemned the attacks and suggested the security forces themselves were behind it to justify an even wider crackdown. It said the bombings were "a prelude to unjust, dangerous decisions."
Friday's violence began around 6:30 a.m. when a vehicle packed with explosives went off outside the capital's main police headquarters in a downtown square, killing at least four people and sending billows of black smoke into the sky. The Health Ministry said in a statement that four policemen were killed and nearly 50 people wounded.
Several police officers sat on the sidewalk weeping outside the building as ambulances rushed in. A blanket covered a corpse on the ground.
The blast dug a deep crater into the pavement, and the street was littered with vehicle parts, shattered glass, bricks and stones. The seven-story facade of the security headquarters was wrecked, with air conditioning units dangling from broken windows. A nearby courthouse and shops were also damaged.
Authorities initially characterized the attack as a suicide bombing, but later investigations suggested the bombers may have escaped before the blast. Security officials close to investigation said that three to five people pulled up the headquarters in two vehicles -- a car and a pickup truck loaded with explosives. The truck's drivers appeared to have fled in the second car before detonating the truck by remote control, they said, speaking on condition of anonymity because they were not authorized to release the information.
Abdullah el-Sayyed, a 26-year-old salesman who lives behind the headquarters, said he was woken up by the blast, followed by heavy gunfire. He described policemen in panic.
"They were devastated. They were firing their guns in panic as if to call for rescue," he said. He added that he plans to return to his home village in Fayoum south of Cairo because he no longer feels safe. "It's not worth it anymore to stay here. Every day I ride the metro and go past here," he said.
The explosion also heavily damaged the renowned Museum of Islamic Art, on the other side of Bab el-Khalq Square. Windows were blasted out all the way up the facade of the building, which was built in 1881 and recently underwent a multimillion-dollar renovation. The antiquities minister, Mohammed Ibrahim, said artifacts inside were damaged, including a rare collection of Islamic art objects and that the museum will have to be rebuilt.
About two hours later, another bomb struck a police car on patrol near a metro station in the capital's Dokki district on the other side of the Nile River, killing one person and wounding eight others, security 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, the officials said. They spoke on condition of anonymity because they were not authorized to speak to the media.
Ahmed Ghaith, a retired army officer who witnessed the blast, said he was waiting for a bus when the blast tore down an advertisement placard and dirt spread everywhere.
"No one killed or injured, not even a cat. We know ... they will get nothing at the end," he said, blaming the Brotherhood.
The violence comes as both the Brotherhood and military supporters are gearing up for rallies on Saturday, three years to the day that protesters first took to the streets in the 18-day uprising the brought down Mubarak.
Islamists are trying to use Saturday's anniversary to build momentum in their campaign of protests to "break the coup." Military supporters, in turn, aim to show broad popular support for the government and el-Sissi.
Brotherhood supporters held protests Friday in several cities around the country on Friday, including in a southern suburb of Cairo and the Mediterranean coastal city of Alexandria. Clashes erupted between the protesters and security forces in the Nile Delta city of Damietta and the central city of Beni Suef, leaving a total of three dead.
The wave of militant attacks since Morsi's fall has largely targeted the military and police, though civilians have also been killed.
The most prominent pervious 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.
An al-Qaida-inspired group, Ansar Beit al-Maqdis, or the Champions of Jerusalem, has claimed responsibility for most of the attacks, saying they aimed to avenge the killings of Morsi's supporters in the post-coup crackdown.
On Thursday, the group posted an online audio message by a man named Abu Osama el-Masri, urging Egyptian Muslims to "rise up against tyranny."
The message warned soldiers and policemen that "obedience to your commanders will not be an excuse before God ... we will target you as we target your commanders."