A bomb has targeted the convoy of Egypt's Interior Minister Mohammed Ibrahim but the minister was unhurt, security forces say.
The explosion took place at around 10:30am (08:30 GMT) on Thursday near Ibrahim's home in the Nasr City area, they said.
What happened today is not the end but the beginning
The minister later appeared on Egyptian state TV to denounce the apparent attempt on his life as a "cowardly assassination bid".
Responding to a question on whether the attack marked the start of "a new wave of terrorism", Ibrahim said: "What happened today is not the end but the beginning".
He added that citizens needed to take care.
State TV reported that the bomb was thrown at the minister's convoy from the top of a nearby building.
At least 21 people were reported injured in the blast, which media reports described as an assassination attempt.
The blast damaged stores and several cars parked on the street and shattered the windows of several nearby apartment buildings. The aftermath of the blast suggested a powerful explosion, with three badly damaged SUVs, including the minister's, and a small raging fire.
The blast site was littered with debris, including tree branches severed by the explosion. Police were searching for suspects in the area but no arrests had been made, security officials said. They spoke on condition of anonymity because they were not authorised to speak to the media.
Officials involved in the investigation told the Associated Press that early results showed that a parked car was laden with explosives and blew up when Mohammed Ibrahim's convoy passed.
Persistent death threats
"Forensic teams have been on the scene looking for clues," reported Al Jazeera's correspondent in Cairo, who we are not naming for security reasons.
"We haven't got other confirmed sources telling us exactly how the explosion happened, but it was a clear attempt to target Muhammad Ibrahim and he is warning that it is just the start of more to come. [...]
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"In the last [few] days, [the] Interior Minister said he had received death threats, so he was already travelling in a well-secured armed convoy."
The Egyptian cabinet responded to the attack by saying that it would strike with "an iron hand those who threaten national security until stability returns" to the country.
"The cabinet insists that this criminal act will not prevent the government from confronting terrorism with force and determination," a cabinet statement said.
The bombing comes amid a violent crackdown since last month on supporters of ousted president Mohamed Morsi by the Interior Ministry police.
Ibrahim has been among those responsible for the violent crackdown.
Hundreds of people were killed in Cairo's Rabaa al-Adawiya and Nahda squares on August 14 when police stormed protest camps set up by Morsi's supporters.
Senior Muslim Brotherhood leader Amr Darrag condemned the assassination attempt on Ibrahim shortly after the attack took place on Thursday.
"The bombing allegedly targeting the minister of interior today is regrettable and the alliance strongly condemns it," Darrag said in a statement on behalf of the Anti-Coup Alliance.
Morsi was ousted by the military on July 3 after popular street protests against his one year rule, and the Anti-Coup Alliance, led by his Muslim Brotherhood, has organised weeks of mass protests against the move.