An Egyptian policeman was killed and four wounded by a roadside explosive near the Cairo suburb of Maadi on Sunday, the Interior Ministry said in a statement.
"At around 12:45 a.m. on June 18 as a vehicle belonging to the Central Security Forces transported a group of officers and conscripts an improvised explosive device planted on the roadside went off," the ministry said.
"This led to the martyrdom of First Lieutenant Ali Abdelkhaliq and the injury of four others, an officer and three conscripts, who have been taken to hospital for treatment."
The bomb was detonated remotely, and an initial examination suggested it was detonated using a mobile phone SIM card, a senior Interior Ministry official told state news agency MENA.
A joint task force made up of several police units is questioning tenants of flats overlooking the site of the attack to try to identify and arrest the culprits, the official said.
There was no immediate claim of responsibility by any group.
Egypt faces an Islamist insurgency led by Daesh group in North Sinai, where hundreds of soldiers and police have been killed since the 2013 ouster of Islamist president Mohamed Morsi.
The group has also increasingly carried out attacks in the mainland on security forces and Coptic Christian civilians in recent months.
Other militant groups, which the government says are linked to the Muslim Brotherhood, are active in Cairo and other cities where they have targeted security forces, judges, and pro-government figures.