Egypt crisis: Police chief dies in Cairo bombings
A police brigadier-general was killed and at least five people were injured when three bombs went off near Cairo university, officials said.
A group calling itself Ajnad Misr, or Soldiers of Egypt, said it was behind the attack.
The first two bombs went off within minutes of each other, with the third exploding about two hours later.
There has been a rise in militant attacks on government targets since the Muslim Brotherhood was ousted in 2013.
The government says militants have killed almost 500 people since last July, most of them policemen and soldiers.
There have been fears of an increase in violence in the run-up to the presidential election in May, correspondents report.
Ajnad Misr issued a short statement, saying it was targeting police officers involved in mass killings of protesters, the Associated Press reports.
The little-known group said the attack also came in response to increased detentions of female demonstrators.
Wednesday's explosions happened near a riot police post outside the main gate of the university's faculty of engineering.
The blasts were reported to have been caused by improvised explosive devices.
State TV named the dead officer as Tariq al-Mirjawi, the head of Giza's investigation department.
"I was waiting for the bus when I heard two explosions. There was dust in the air and policemen were screaming" an eyewitness told AFP.
The third explosion took place as journalists and emergency workers attended the scene, but was reportedly much smaller than the first two and caused no casualties.
The BBC's Orla Guerin in Cairo says the area around the university has become a battleground for clashes between police and student supporters of the banned Muslim Brotherhood in recent weeks.
The military-backed interim government outlawed the movement at the end of last year, declaring it a terrorist organisation.
It accuses the movement of supporting attacks against the police and army - a claim the Brotherhood strongly denies.
Since the overthrow of the Brotherhood-linked President Mohammed Morsi, more than 1,000 people have been killed and thousands of members have been detained in a crackdown by the interim authorities.