Four people were wounded on Friday by a bomb planted at a Cairo intersection near the Pyramids, the interior ministry said, and the Islamic State (IS) group claimed it had planted the device.
Separately in Sinai, where the IS group is waging an insurgency, a roadside bombing killed a police officer and wounded three others in the town of El-Arish, the ministry said.
The Cairo bomb went off at the Rimaya intersection, close to several hotels and 1.5 km (just under a mile) from the Pyramids, it said.
It detonated when police used water cannon to try to defuse it, injuring two policemen and two hotel security guards.
One of the police was critically wounded, a security official said.
In its statement, circulated on social media sites, the Islamic State group said it had set off the Cairo bomb to target "the apostate police force."
Militants in the Sinai Peninsula pledged allegiance last year to the Islamic State group, which controls parts of Iraq and Syria.
The Islamist insurgency in the peninsula has swelled since the army's ouster of Islamist president Mohamed Morsi in July 2013.
Militants loyal to IS have killed hundreds of Egyptian soldiers and policemen, mostly in North Sinai.
A government crackdown targeting Morsi's Muslim Brotherhood movement since 2013 has left hundreds dead and thousands jailed.
Hundreds more, including Morsi himself, have been sentenced to death, often in mass trials. Many have appealed and won retrials, while seven have so far been executed by hanging.