Islamic State's Egypt affiliate said it was behind a car bombing that wounded 29 people near a state security building and courthouse in a Cairo suburb early on Thursday.
A statement circulated on Twitter by supporters of the group, Sinai Province, said the bomb was a reprisal for the execution of six of its members convicted of carrying out an attack north of the Egyptian capital last year.
"Let the apostates of the police and army, the followers of Jews, know we are a people who do not forget our revenge," the statement said.
In May, Egypt executed six members of Sinai Province for attacking soldiers near Cairo in 2014. The men were convicted on charges which included carrying out an attack in which two army officers were killed in Arab Sharkas village north of Cairo.
Sinai Province has killed hundreds of soldiers and police since the military toppled President Mohamed Morsi of the Muslim Brotherhood in 2013 after mass protests against his rule.