CAIRO - An Egyptian judge in one of the trials of ousted Islamist president Mohamed Morsi escaped unharmed when a car bomb exploded in Cairo on Friday, police officials said.

The officials said the bomb in the eastern Nasr City district had targeted judge Ahmed Abul Fotouh as he was driving by, adding that the blast injured no one. The attack came days after a roadside bombing targeting a police convoy in Cairo killed a passerby.

Meanwhile, Egyptian authorities said on Friday they had arrested members of two recently emerged militant groups, along with weapons, explosives and evidence that the organisations had been set up by the Muslim Brotherhood.

Police detained five leaders and other members of the Hasam Movement and Louwaa al-Thawra, the Interior Ministry said - both groups that have claimed responsibility for assassination attempts on judges, policemen and military officers.

There was no immediate comment from either organisation, or from the outlawed Muslim Brotherhood, which says it is a peaceful movement and accuses the government of abuses.

The Brotherhood won Egypt 's first free elections after the 2011 uprising that ended Hosni Mubarak's 30-year rule.