At least five other people were injured in the attacks, the authorities say.

The first two bombs went off within minutes of each other, with the third coming about two hours later.

Egypt has witnessed several attacks against government targets by militant groups following the ousting of the Muslim Brotherhood last July.

The government says militants have killed almost 500 people since last summer, 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.

The latest explosions happened outside near a riot police post outside the main gate of the university's faculty of engineering.

Officials said police had been the targets of the blasts, which were reported to have been caused by improvised explosive devices.

Egyptian security forces stand guard outside Cairo university after the blasts

Smoke is seen rising shortly after the first two bombs struck

Investigators inspect the scene of the bombings near the police post

State TV named the 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 university has been the site of clashes between police and students supporting the Brotherhood

Militants have stepped up their campaign of violence against Egyptian police 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.