A bomb blast near the Egyptian foreign ministry killed two policemen on Sunday, state television said.
A Reuters witness earlier heard a blast in the area and smoke was seen rising briefly from the neighbourhood where the foreign ministry is located.
Sirens were heard and people were running.
The explosion occurred on a sidewalk in the neighbourhood of Boulaq Abu Eila, under the May 15 Bridge, according to state television and the state news agency.
Bombings and shootings carried out by Islamist militant groups have killed hundreds of Egyptian police and soldiers since the army toppled President Mohamed Mursi of the Muslim Brotherhood last year.
Security officials say ties have been established between Islamic State, the al Qaeda offshoot that controls parts of Iraq and Syria, and Egypt’s most lethal militant group, Sinai-based Ansar Bayt al-Maqdis.