The assassination attempt against Mohammed Ibrahim, who is in charge of the police force, fueled concerns over a possible wave of violence in retaliation for the July 3 ouster of Mohammed Morsi and the ensuing crackdown on Islamists.
The blast wounded at least 22 police and civilian bystanders and heavily damaged three vehicles in Ibrahim's convoy -- though he survived unhurt. Security officials said initial investigations showed it came from a parked car loaded with explosives in the trunk. They spoke on condition of anonymity because the probe was not yet complete.
The attack echoed the sort of insurgency-style methods that Islamic militants have increasingly used in Egypt's tumultuous Sinai Peninsula. Last month, militants there attempted a suicide car bombing but were killed by police before carrying it out.
The bombing also harkened back to the insurgency waged by Islamic militants in the 1980s and 1990s against the rule of now-ousted autocrat Hosni Mubarak.
At that time, militants targeted several senior officials, killing the parliament speaker and attempting to assassinate at least four successive interior ministers, the last in 1993. Mubarak himself survived an assassination attempt in 1994, when militants attacked his convoy in Addis Ababa, Ethiopia.
Some of Morsi's more hard-line supporters have publicly threatened to wage a campaign of assassinations and car bombings against officials of the military-backed government until the former president is reinstated.
There was no immediate claim of responsibility for Thursday's blast.
The Anti-Coup Coalition, which groups Morsi's Muslim Brotherhood and other allied Islamist factions, condemned the attack, saying "it is against any violent act, even if it is against those who committed crimes against the people, because we aim to uphold the law."
It warned that authorities will use the blast as a pretext to extend a state of emergency in place since Morsi's removal and to increase "oppression" and arrests of Islamists.
The explosion detonated in the late morning as Ibrahim's convoy passed through Nasr City, an eastern district of Cairo that is a stronghold of the Brotherhood. Among those wounded were 10 police and 11 civilians, including a 7-year-old child whose right leg was amputated, the security officials said.
A mangled body was found near the suspected bomb car and investigators were working to determine if it was of a bystander, a bomber or perhaps a lookout tasked with alerting the convoy's approach, the officials said.
The blast left a main avenue in Nasr City strewn with charred skeletons of vehicles, and a fire in one poured out heavy black smoke. Nearby shopfronts were mangled and windows of nearby apartment buildings were shattered.
Clearly shaken, Ibrahim said on state television that his car, a black SUV, was directly hit by a "large-size explosive device" that badly damaged it along with four other vehicles in the convoy.
"It was a heinous (assassination) attempt," he later told reporters at the Interior Ministry in central Cairo. The explosive device, he added, likely was detonated by remote control.
"Even if I am martyred, another minister of interior will come and continue the war on the evil terror until we secure the country," Ibrahim said.
Police searched the area for suspects but no immediate arrests were made, the security officials said.
Ibrahim has aggressively led the crackdown on Islamists. Not far from the bomb site in another part of Nasr City, police stormed a sit-in protest by Morsi supporters on Aug. 14, killing hundreds.
Hundreds of members of Morsi's Muslim Brotherhood and other Islamists have been arrested since the coup, including the Brotherhood's top leader Mohammed Badie and his powerful deputy Khairat el-Shater. Morsi has been held in an undisclosed location.
Ibrahim said in a television interview last week that he had received death threats.
Ibrahim was appointed to his post by Morsi and came under sharp criticism at the time even by some in the police as too beholden to the Islamist president. But since the coup, he has fully embraced the new military-led leadership.
Morsi, Egypt's first freely elected president, was toppled after days of protests by millions of Egyptians who demanded his departure after a year in office. During the six-weeklong sit-in protest in Nasr City, many of his supporters said they would fight the military-backed government al-Qaida-style, with suicide bombings, roadside bombs and assassinations.
The military chief who toppled Morsi, Gen. Abdel-Fattah el-Sissi, issued a statement pledging to continue the fight against terrorism and stating the armed forces' support for the police.
Prime Minister Hazem el-Beblawi also condemned the "criminal" attack and vowed his government will "decisively and forcefully" combat terrorism.
The office of interim President Adly Mansour vowed in a statement that it would "not allow the terrorism that the Egyptian people crushed in the 1980s and 90s to raise its ugly head again."
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