Egypt on Thursday arrested a leading Muslim Brotherhood member who played a key role in negotiations between his now-banned group and the government. In Cairo, at least nine people, including five policemen, were hurt in incidents involving a home-made bomb and a stun grenade.

The early morning arrest of Mohammed Ali Bishr from his home in the Nile Delta was linked to a call for demonstrations at the end of the month, according to a security official. The rallies have been called by a hard-line Islamist group called the Salafi Front, and not the Brotherhood.

Egypt has waged a sweeping crackdown on the Brotherhood since the military ouster in July 2013 of President Mohammed Morsi, a senior official with the Islamist group, following mass demonstrations demanding his resignation. Morsi is among tens of thousands of Brotherhood members who have been detained in the clampdown, while hundreds have been killed.

In apparent retaliatory attacks, Egypt has seen a surge in bomb attacks. And while large suicide bombings usually target the police and the military, small-scale attacks with grenades and home-made explosive devices planted on trains, at universities and near police stations, are more frequent.

On Thursday, a stun grenade on a train at Cairo's main Ramses Square station set off panic and a stampede in which four people were hurt, another security official said. Both officials spoke on condition of anonymity because they were not authorized to speak to the media.

And in southern Cairo, unidentified assailants hurled a home-made bomb at security forces standing guard outside Helwan University, wounding five policemen.

Militant group Ajnad Masr, or "Soldiers of Egypt," took responsibility for the attack in a statement posted on its official Twitter feed. The statement warned that it considers "administrative security at universities" and private companies doing the work of "tyrants" to be legitimate targets for attack.  It said the attack was in response to the arrest and assault of female students.