A recently-emerged militant group called the Hasm Movement claimed responsibility on Friday for an assassination attempt on a senior Egyptian prosecutor, saying it was in revenge for death sentences handed to thousands of convicts.
The organisation, which has claimed four other attacks since July, said it set off the car bomb that exploded near a vehicle carrying assistant prosecutor general Zakaria Abdel Aziz from his office to his home in Cairo on Thursday.
He and his entourage were not hurt but one passerby was wounded.
Hasm, the Arabic word for decisiveness, accused judges of sentencing thousands of innocent defendants to death, or jailing them for life, at the behest of the military. "You will face justice," it said in a statement that mixed Islamist and anti-government political rhetoric.
Egypt is facing an Islamist insurgency led by Islamic State's branch in North Sinai, where hundreds of soldiers and police have been killed.
Judges and other senior officials have increasingly been targeted by radical Islamists angered by hefty prison sentences imposed on members of the now-outlawed Muslim Brotherhood.
The Brotherhood, which says it is a peaceful organisation, won Egypt's first free elections after the 2011 uprising that ended Hosni Mubarak's 30-year rule.
But its presidential candidate, Mohamed Mursi, was himself deposed after mass protests against his rule and replaced by general turned President Abdel Fattah al-Sisi in 2013.
Sisi has since overseen a crackdown on opposition in which hundreds of Brotherhood supporters were killed and thousands, including Mursi, jailed or sentenced to death.
Hasm's statement on Friday included several photographs of what appeared to be Abdel Aziz's car with the caption "target's car" as well as his house and guards.
Hasm has also said it was behind an assassination attempt last month on Egypt's former Grand Mufti, Ali Gomaa, once one of the country's top religious authorities.
Gomaa is an outspoken critic of Islamist groups, including the Muslim Brotherhood, and in his previous job had the final say on whether to confirm death sentences.