Azbakiya's top prosecutor Mohamed Hetta ordered crime lab experts to examine the site of late Tuesday night's blast in El-Issaf Square near the High Court building to determine the nature of the device used in the attack and assess the damage.
A team of investigators led by the chief public attorney for north Cairo, Wael Hussein, continued their examination of the scene at dawn Wednesday.
Some members of the team have been sent to Al-Helal and El-Qubbah Military hospitals to listen to the initial testimonies of the injured receiving treatment there.
The number of injured from the blast has risen to 13, chief of the Health Ministry's Ambulance and Emergency Care Department Mohamed Soltan said.
He told MENA that three of the victims are in critical condition.
He said that he checked on the other cases at El-Helal Hospital and their injuries vary, ranging from medium to slight.
The Interior Ministry had said on Tuesday that the blast that hit downtown Cairo at 11:15 p.m. in the El-Isaaf Square resulted from an explosive device planted beneath the walkway's metal wall, leaving a dozen injured.
Firm security measures have been enforced and investigations are underway to identify the perpetrators, a media official at the ministry said.
Civil defense teams mopped up the area to find if there were more explosives, he added.