* Army-backed government and Muslim Brotherhood in standoff
* Protests test Brotherhood's remaining power
* Constitutional amendments would ease restrictions on Mubarak-era figures
Supporters of Egypt's deposed President Mohamed Mursi called for mass protests on Friday against the army takeover, in a test of the Muslim Brotherhood's ability to bring out the crowds with many of its leaders now behind bars.
Egyptians are enduring the bloodiest crisis of their modern history after the military overthrew Mursi on July 3 following demonstrations against his rule. It dispersed his supporters' protest camps on Aug. 14 and launched a campaign of arrests that has already netted the group's general guide Mohamed Badie.
At least 900 people, including 100 soldiers and police, have been killed in the crackdown on Mursi supporters in the past week, according to government sources. Brotherhood supporters say the real figure is far higher.
The clampdown appears to have weakened the Arab world's oldest and arguably most influential Islamist group, which won five successive elections in Egypt following the 2011 uprising that swept Mursi's predecessor, Hosni Mubarak, from power.
Pro-Mursi protests have fizzled out over the past week. The muted reaction to the release of Mubarak on Thursday highlighted the growing power shift in favour of the military he once commanded.
Brotherhood supporters have nevertheless called on Egyptians to hold marches on the weekly Muslim prayer day, billed as a "Friday of Martyrs", against the army takeover.
"We will remain steadfast on the road to defeating the military coup," a pro-Mursi alliance called the National Coalition to Support Legitimacy and Reject the Coup said in a statement. It named 28 mosques in Greater Cairo as points of departure for the protests.
Mubarak was flown from jail on Thursday in a symbolic victory for the army-dominated old order that has imprisoned his freely-elected Islamist successor.
A blue-and-white helicopter took Mubarak from Cairo's Tora prison, where scores of his supporters had gathered to hail his release. He was flown to a military hospital in the nearby southern suburb of Maadi, officials said.
For Mubarak's enemies, the moment marked a reversal of the 2011 uprising that brought him down as one of the pillars of authoritarian rule in the Middle East.
Mubarak's release plays into the Brotherhood's argument that the military is trying to rehabilitate the old order. The army-installed government casts its conflict with the Islamist movement as a life-or-death struggle against terrorism.
"This is the end. Mubarak will never be an important political player, but symbolically, it's a victory dance by the reconstituted old state," said Joshua Stacher, an Egypt expert at Kent State University in the United States.
Adding to a sense among some activists that the freedoms won in the 2011 revolt are in danger, planned amendments to the constitution leaked to the media this week appear designed to place limits on political parties and ease restrictions on the participation of Mubarak-era officials in politics.
But some Egyptians, many of whom have rallied behind the army's crackdown, expressed fondness for the 85-year-old former air force commander whose tight grip on power brought stability.
"He protected the country," said Lobna Mohamed, a housewife in the crowd of Mubarak well-wishers. "He is a good man, but we want (Abdel Fattah) Sisi now," she said, referring to the army commander who overthrew Mursi following large demonstrations.
Mubarak was sentenced to life in prison last year for failing to prevent the killing of demonstrators. But a court accepted his appeal earlier this year and ordered a retrial in the case, for which he has already served the maximum amount of pretrial detention. Mubarak was arrested in April, 2011.
The military's declared plan for a return to democracy has yet to calm the most populous Arab nation, where security forces impose a nightly curfew as they hunt down Brotherhood leaders.
Alarmed by the bloodshed, the United States and European Union are reviewing their aid to Cairo.
Saudi Arabia, an enemy of the Brotherhood, has promised to cover any shortfall. It and other rich Gulf Arab states have already pledged $12 billion since Mursi's fall.
EU foreign ministers stopped short of agreeing immediate cuts in aid to Egypt on Wednesday, in part because of concern that doing so could damage any future EU mediation effort.
An EU attempt to broker a compromise collapsed before security forces cleared out the Brotherhood protest camps.
James Moran, the bloc's ambassador in the Egyptian capital, described reconciliation prospects as a huge challenge.
"Passions are high, emotions are high. Things have to cool off a little bit," he said.
"It would be good if this is not all painted one colour. There may be different strains of opinion within the Islamist movement," he said. "One thing is for sure - the Islamist constituency is there, and you are going to have to find a way somehow of living with it."
A senior United Nations official, Jeffrey Feltman, met interim Prime Minister Hazem el-Beblawi on Thursday as part of an effort to promote peace and reconciliation.
The government has bristled at foreign attempts to use aid or persuasion to nudge it to seek a political compromise.