Egypt's Muslim Brotherhood on Friday held protests against the military, despite a relentless clampdown on Islamists, dpa reported.
Hundreds of backers of toppled Islamist president Mohammed Morsi marched from mosques in Cairo and its twin city of Giza, chanting slogans against army chief Abdel-Fattah al-Sissi.
Some demonstrators banged on empty pots and shouted slogans denouncing a dusk-dawn curfew in force as part of a state of emergency declared by the military-backed authorities last week.
Police fired tear gas to disperse pro-Morsi demonstrators in the Nile Delta city of Mansura, reported state-run newspaper al-Ahram.
It added that at least 25 people were injured in clashes between Morsi's backers and opponents in the Delta city of Tanta.
Police arrested 20 Brotherhood followers for illegally possessing arms in Tanta, according to al-Ahram.
Other pro-Morsi protests were held in the southern cities of Assiut and Fayyoum, which are Brotherhood strongholds.
Morsi's overthrow on July 3 plunged Egypt into a crisis, which deepened after security forces killed hundreds of his supporters in a crackdown that started with the breaking up of two protest camps in Cairo.
Hundreds of Morsi's backers, including top Brotherhood leaders, have been rounded up since his toppling.
The release from detention of Hosny Mubarak this week added to fears that the military was seeking to revive the former president's regime, more than two years after the revolt that ended his 30-year rule.
The secular April 6 Youth Movement, meanwhile, said it had cancelled a protest planned for Friday in Cairo against Mubarak's release.
The movement, which led a 2011 uprising that forced Mubarak to step down and backed the army's removal of Morsi, said it had called off the rally to avoid clashes with Brotherhood supporters.
Mubarak, 85, was released from detention on Thursday and taken to a military hospital in Cairo to serve house arrest.
He faces a retrial on charges of killing protesters during the uprising against his rule.
US President Barack Obama, meanwhile, appeared to rule out cutting more than 1 billion dollars in annual military aid to Egypt over the killing of hundreds of Islamists in the crackdown.
"Aid itself may not reverse what the interim government does," he said in an interview with CNN.
"I think what most Americans would say is that we have to be very careful about being seen as aiding and abetting actions that we think run contrary to our values and our ideals."
Obama said his administration was currently "doing a full evaluation of the US-Egyptian relationship."
He added: "No doubt that we can't return to business as usual, given what's happened."
"There was a space right after Mr. Morsi was removed in which we did a lot of heavy lifting and a lot of diplomatic work to try to encourage the military to move in a path of reconciliation," said Obama. "They did not take that opportunity".
Obama last week cancelled US-Egyptian military exercises that were planned for next month. The United States has also delayed delivery of four F-16 aircraft over the unrest.