Click here for the latest news and analysis on Egypt.

Cairo has seen several homemade bomb attacks in recent months, though they have typically targeted security forces. Thursday's blast appeared to be the first targeting civilians. Last month Mohamed Mabrouk, a lieutenant colonel in the state security service, was killed near his home in Nasr City. Interior Minister Mohammed Ibrahim survived an assassination attempt in the neighborhood in September.

Thursday's blast came hours after the interim government labeled the Muslim Brotherhood a "terrorist organization" and froze the assets of charities linked to the group.

Egyptian authorities have arrested 23 Muslim Brotherhood supporters Thursday on accusations of belonging to a terrorist organization.

The people arrested were accused of passing out leaflets in support of the Brotherhood, promoting the group's ideology, and inciting violence against the Egyptian security services, according to Egypt's state media agency, MENA.

Interior Ministry spokesman Hany Abdel Latif told state TV that anyone taking part in Brotherhood protests will be jailed for five years. Jail terms for those accused under the terror law stretch up to life imprisonment.

"The sentence could be death for those who lead this organization," he said.

Terrorism charges will also apply to anyone who finances or promotes the group "verbally and in writing." Publication of the Brotherhood's newspaper, Freedom and Justice, was halted in response to the decision.

"Egypt will stand firmly in confronting terrorism and the people will never be afraid as long as the army is present," said Egyptian army chief General Abdel Fattah el-Sisi, during an army graduation ceremony on Thursday in Cairo.

On Wednesday, the Sinai-based group Ansar Beit al-Makdis claimed responsibility for the Mansoura bombing in a statement posted online. Numerous attacks have killed dozens of soldiers and police officers in the Sinai over the past few months.

Despite Ansar Beit al-Makdis' claim, the government nonetheless pinned the blame on the Brotherhood. The Brotherhood has denied any involvement, saying the government is trying to scapegoat it, and called for increased protests. Authorities are facing mounting criticism that they have not done enough to restore security following months of political turmoil.

"The police and the army, they are the biggest powers in the country, and they have one responsibility, to protect the people," said Tarek Ezzedine, who witnessed the explosion. "They need to do their job."

Al-Azhar University has for months been the site of near-daily protests by student supporters of President Mohamed Morsi, who was ousted in a military coup in July. The university, and the bombing site, are down the road from Raba'a al-Adawiya square, one of two locations where hundreds of pro-Morsi protesters were killed by police in August.

Hany Abdellatif, a spokesman for the interior ministry, said the bombing was meant to instill fear ahead of a January referendum on Egypt's new constitution. The Muslim Brotherhood opposes the referendum and has carried out small protests daily calling for the reinstatement of Morsi.

Al Jazeera and wire services