A small bomb went off Tuesday evening on a bridge in the Egyptian capital without causing any casualties, a security official said.
The explosion in central Cairo caused only minor damage to the bridge's handrail, the official said.
Since the military ousted Islamist president Mohamed Morsi in July, militants have carried out scores of attacks, including several bombings, targeting security forces.
Attacks on civilian targets have remained rare in Egypt, but on Saturday a homemade bomb exploded at a tram station in eastern Cairo, wounding one person.
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In February, a suicide bomber targeting a tour bus near the Taba border crossing with Israel in Sinai killed three South Koreans.
An Al-Qaeda inspired group, Ansar Beit al-Maqdis (Partisans of Jerusalem), claimed the attack.
The jihadist group has claimed responsibility for several high-profile attacks, including a car bombing at a police headquarters in Cairo and the shooting down of a military helicopter in the Sinai Peninsula.
The Sinai-based group said the attacks were in revenge for a deadly crackdown by the security forces on Morsi's Islamist supporters.
More than 1,400 people have been killed in the crackdown, according to Amnesty International. Thousands have been jailed.