A midday bomb blast in one of the busiest boulevards in Cairo's business district has killed two civilians, according to the health ministry.
Nine others, including policemen, were injured in Monday's explosion outside the Egyptian High Court, the ministry said.
Shortly after the blast, a little-known group claimed responsibility for the attack.
The bomb was hidden under a car parked near the country's highest criminal court in Cairo's Ramses neighbourhood.
The area is very crowded, with dozens of street vendors selling their ware on stalls set up on the asphalt. Nearby are several bus stops, a railway station and a metro station.
Egyptian private The Seventh Day TV broadcast footage of the site, showing hundreds of onlookers around cars with smashed windows and blood on the pavement.
Police cordoned off the area and state TV later reported that a second bomb was dismantled before it went off.
A group calling itself Revolutionary Punishment claimed responsibility on its Twitter account for the attack, saying they targeted a police checkpoint.
The group is believed to mostly consist of political activists seeking revenge for the ongoing crackdown on ousted President Mohamed Morsi's supporters.
Morsi's Muslim Brotherhood group has been branded as a "terrorist organisation" and hundreds of its members are either underground, on the run, or in jail awaiting trial.
Egypt has seen a wave of attacks, mostly targeting the country's security forces, since the military toppled Morsi in July 2013.
On Sunday, a bomb went off near a police station in the southern city of Aswan, killing two civilians and wounding a soldier and four others.
Most of the bombings in Cairo have been rudimentary and caused no casualties. But several have killed policemen, including two senior officers who died while trying to defuse bombs planted outside the presidential palace last June.
Those bombs and several others that killed policemen in Cairo were claimed by the Ajnad Misr (Soldiers of Egypt) armed group.
A Sinai-based armed group, which has pledged allegiance to Islamic State of Iraq and the Levant (ISIL) group fighting in Syria and Iraq, has claimed responsibility for several suicide bombings and larger attacks.
On January 29, simultaneous car bombings and mortar attacks on security headquarters in the Sinai Peninsula killed at least 30 people, most of them soldiers.
The attacks have raised security concerns in the run-up to a major economic conference in Egypt later this month, aimed at attracting foreign investment.