A bomb exploded outside the gates of Cairo University on Wednesday, an Egyptian police official said, wounding at least nine people including policemen.

Police cordoned off the area and scoured it with sniffer dogs. An official said five of the nine wounded were policemen stationed outside the campus to quell protests.

The blast took place near the site of a bombing in April that killed a police general, and where the riot policemen are now stationed on foot and in armoured vehicles to confront the frequent protests by pro-Islamist students.

The police official said the explosion came after policemen had clashed with student protesters earlier in the day.

April's attack was claimed by Ajnad Misr, a militant Islamist group that has killed several policemen in bombings around Cairo.

The group has said its attacks were in response to a deadly police crackdown on Islamists following the overthrow of president Mohamed Morsi last year.

It pledged retaliation last week after police quashed protests in several universities across the country.

A student in Alexandria University later died of gunshot wounds sustained during the clashes.