A third blast struck on Wednesday outside Cairo University, one of the most prominent and oldest universities in Egypt, after earlier twin blasts left a police top official killed and other five officers wounded in the same area, state-run Nile TV reported.

The third bomb was planted on a tree near the main gate of the university. No injuries have been reported from the blast yet.

A few hours before the three blasts, the security forces arrested seven members of the outlawed Muslim Brotherhood organization and captured eleven bombs and automatic weapons in their possessions, state-run Ahram newspaper reported on its website.

The three blasts hit the security checkpoint outside the university in Nahda square, one of the basic sit-ins venues for the supporters of the ousted president Mohamed Morsi.

Since the ouster of the Islamist leader by the army last July, wave of explosions hit the restive Sinai Peninsula against security men and their premises. Lately, the blasts moved to the capital and the Nile Delta cities.

A recent governmental report said the death toll from such attacks reached nearly 500 people, most of them soldiers and police.

The army has launched a large-scale operation since Morsi's removal to uproot the crime hideouts in the restive Sinai. The al- Qaida-inspired Ansar Beit al-Maqdis group claimed responsibility for most of the attacks.