A homemade bomb exploded near a traffic police post on a bridge over the Nile River in Cairo early Tuesday, wounding two policemen and a civilian.
Officials said the rush-hour blast targeted a security checkpoint near al-Galaa bridge in central Cairo.
Militants have carried out a series of bombings and shootings since the army ousted democratically-elected president Mohamed Morsi of the now-banned Muslim Brotherhood last July. Most of the attacks have taken place in the restive Sinai Peninsula, but have spread to other cities, including Cairo.
On Monday, a student was killed in clashes between police and Morsi supporters at Cairo University, a medic said, in an anti-government protest.
Security forces fired teargas at protesters who in turn hurled fireworks and at least two petrol bombs at police lines, a Reuters reporter said. A reporter for a local newspaper was wounded when he was hit by birdshot, the paper said.
With the state cracking down hard on the Muslim Brotherhood, the universities have become the last major arena for protests by supporters of Morsi.
Earlier this month, the government said such attacks have killed nearly 500 people, most of them soldiers and police.
Security forces have also carried out a deadly crackdown on Morsi's supporters and arrested many Brotherhood leaders. Clashes between protesters and security forces have left more than 1,000 people dead, most of them Morsi supporters.