State Department spokeswoman Jen Psaki said the United States agreed with Germany's earlier appeal for Morsi to be released and was "publicly" making the same request.

The deposed president has been held in a "safe place," according to Egypt's interim leaders, and has not been seen in public since his ouster on July 3.

Psaki said US officials had been in regular contact with all sectors of Egyptian society, and Washington was echoing German calls for "an end to restrictions on Mr Morsi's whereabouts".

A German foreign ministry spokesman said a "trusted institution" such as the International Committee of the Red Cross should be granted access to Morsi.

As night fell on Cairo, tens of thousands of protesters prayed and broke their fast together on the first weekend of the holy month of Ramadan.

They had spent the day protesting outside the Rabaa al-Adawiya mosque in the Nasr City neighbourhood, holding Egyptian flags and Korans, chanting against the military coup that unseated Egypt's first freely elected president.

"We are here to deliver a message to the military that we won't give up on legitimacy. We will fight for our rights," said protester Ashraf Fangari.

"We are here to defend our votes. They were stolen from us."

Millions of Egyptians had taken to the streets to demand Morsi's resignation -- accusing him of being a puppet of the Muslim Brotherhood and of failing to fulfil the people's aspirations of freedom and social justice.

The mass anti-Morsi demonstrations prompted an army intervention and days of bloody clashes.

"We will continue to resist. We will stay one or two months, or even one or two years. We won't leave here until our president, Mohamed Morsi, comes back," key Islamist leader Safwat Hegazi told Friday's crowd.

Hegazi demanded Morsi's reinstatement, immediate parliamentary elections and a committee to oversee a plan for national reconciliation.

Thousands also massed in support of Morsi outside the University of Cairo, watched over by a heavy security presence.

Despite the defiance, the interim authorities are pressing ahead with forming a new government amid financial help from Gulf states to shore up the faltering economy.

Interim premier Hazem al-Beblawi has decided on 90 percent of his proposed cabinet line-up and would begin talks on Saturday with the nominees, sources told the official MENA news agency.

The ministers of defence and interior in the previous government are due to keep their jobs and that the full cabinet line-up would be finalised by the middle of next week.

The Muslim Brotherhood, which is now in tatters, its leadership detained, on the run or keeping a low profile following Morsi's overthrow, said it will not join the new government.

The onset of the holy fasting month of Ramadan, usually a time of communal sharing and unity, has been marked by tensions after deadly clashes.

Rival demonstrators also rallied in the capital on Friday.

In Cairo's Tahrir Square and outside the Ittihadiya presidential palace, hundreds of anti-Morsi protesters sat down for a festive iftar meal to break the dawn-to-dusk Ramadan fast.

The rallies have raised fears of more of the violence that has shaken Egypt since the army removed Morsi.

In the worst single incident, clashes at an army building in Cairo on Monday killed 53 people, mostly Morsi supporters.

The Brotherhood accuses the army of "massacring" its supporters, while the army says soldiers were attacked by "terrorists" and armed protesters.