Egypt's Muslim Brotherhood said Wednesday that it would join protesters in Cairo to protest the slow-paced trials, reversing their previous rejection of calls by activists to join them, dpa reported.
Pushing for faster changes, including trials of former regime officials, protesters plan a one million-strong strike on Friday in Tahrir Square, the epicentre of last winter's popular revolt against former president Hosny Mubarak.
The Brotherhood, considered Egypt's largest and most organised opposition group, said it had changed its stance due to "injustices suffered by families of martyrs" and the release on bail of officers charged with killing protesters.
On Monday, a Cairo courthouse released on bail 14 police officers who had been accused of killing 17 protesters in the city of Suez during the uprising.
Riots erupted on Wednesday in Suez, around 100 kilometres north-east of Cairo, after the court ruled against the Attorney General's appeal against the officers' release.
Families of those killed during the January 25 revolution and protesters angered by the court's decision, clashed with police forces. Both groups hurled stones at each other and people were trying to attack the security headquarters, activists said.
People were also chanting slogans against the police and the Interior Ministry.
Tensions are now growing in Egypt over the slow pace of trials for police accused of killing protesters during the 18 days of protests that led to the ouster of Mubarak.
The former interior minister and many police officers face prosecution on charges of attacking and killing more than 840 people during the uprising. More than 6,000 people were injured.
While the military was credited with aiding the January revolt, pro-democracy activists have begun to criticize military leaders, accusing them of failing to hold accountable police suspects and of standing in the way of speedy trials for Mubarak and his aides.