Updated 2:35 pm: One person was killed in a third explosion at Cairo University on Wednesday shortly after twin bombs killed a police brigadier general there, security officials said.
There was no immediate claim of responsibility for the violence but Islamist militants have carried out similar operations against police and soldiers.
The attack was the latest by militants targeting security forces following Islamist president Mohammed Mursi's overthrow in July.The first two bombs also wounded five policemen, the interior ministry said, identifying the slain officer as Brigadier General Tarek al-Mergawi.
A police general at the scene told AFP that the first two bombs were concealed in a tree between two small police posts.
"I was waiting for the bus when I heard two explosions. There was dust in the air and policemen were screaming," said a witness, Sakta Mostafa.
A student in Cairo University said he ran out of the campus after hearing the explosions.
"I found a lifeless man in plain clothes and a policeman bleeding from his leg," said the student, Amr Adel.
Mergawi was a chief detective who would have been dressed in civilian clothes.
The government claims militants have killed almost 500 people, most of them policemen and soldiers, in attacks since Mursi's overthrow amid a deadly crackdown on his Islamist supporters.
Most of the attacks have taken place in the Sinai Peninsula, a hub of militant activity, but the jihadists have increasingly targeted police in the capital and the Nile Delta.
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