Islamist parties and movements in Egypt have called on their followers to demonstrate against the military overthrow of the country's first democratically elected leader, Mohamed Morsi.
The National Alliance to Support Legitimacy, which includes the ousted president's Muslim Brotherhood, urged "peaceful protests" on Friday in all of Egypt's provinces to denounce the coup.
It came after the country's top judge, Adli Mansour, was sworn in as interim president.
The chief justice of Egypt's supreme constitutional court, took his oath of office under an army transition plan during a ceremony that was broadcast live on state television.
Shortly afterwards, officials announced they had arrested the supreme leader of the Muslim Brotherhood, the Islamist group of the deposed president.
Mohammed Badie was arrested on Wednesday night in a coastal city west of Cairo and flown to the capital on a military helicopter.
Above Tahrir Square, for days the centre of anti-government protests, Air force planes painted the sky in the colours of the national flag.
"I swear to preserve the system of the republic, and respect the constitution and law, and guard the people's interests," Mr Mansour said.
He praised the mass protests, saying they united Egyptians, but also invited the deposed president's Muslim Brotherhood "to take part in the political life".
"The most glorious thing about June 30 is that it brought together everyone without discrimination or division," he continued.
"I offer my greetings to the revolutionary people of Egypt.
"I look forward to parliamentary and presidential elections held with the genuine and authentic will of the people.
"The youth had the initiative and the noblest thing about this glorious event is that it was an expression of the nation's conscience and an embodiment of its hopes and ambitions. It was never a movement seeking to realise special demands or personal interests," he added.
The ceremony followed the dramatic removal of Mr Morsi by the military, the suspension of the Islamist-drafted constitution and a declaration of fresh presidential and parliamentary elections.
Mr Morsi, who was elected a year ago, remains in custody at an undisclosed facility.
The Muslim Brotherhood, which renounced violence decades ago, said it would boycott the new military-sponsored political process, but vowed not to take up arms, according to a senior leader of the group, Mohamed El-Beltagy.
But he warned that the overthrow might push other groups towards violent resistance.
The "second revolution" - after the Arab Spring uprisings that led to the overthrow of Hosni Mubarak in 2011 - leaves Egypt's 84 million people deeply divided.
In Cairo's Tahrir Square, millions celebrated the news of Mr Morsi's removal with fireworks. At a square near Cairo University, his supporters were stunned into initial silence at the news.
The president's ousting prompted clashes across Egypt that left at least 14 people dead and hundreds wounded.
Fearing a violent reaction by Mr Morsi's supporters, troops and armoured vehicles were deployed across the streets of Cairo and elsewhere, surrounding Islamist rallies.
British Prime Minister David Cameron called for a return to the democratic process.
"We never support in countries the intervention by the military but what now needs to happen … is for democracy to flourish and for a genuine democratic transition to take place," he said.
"All parties need to be involved in that, and that's what Britain and our allies will be saying very clearly to the Egyptians."
Amid a crackdown on Islamist movements, prosecutors sought the arrest of the Muslim Brotherhood's top leaders and of some 300 members of the group and other organisations.
In a televised address, the commander of the armed forces, General Abdul Fatah Khalil al Sisi, said Mr Morsi had "failed to meet the demands of the Egyptian people".
Flanked by military officials, Muslim and Christian clerics and political figures, he unveiled details of a political transition which he said had been agreed with them.
As acting leader, Mr Mansour will be assisted by an interim council and a technocratic government until new presidential and parliamentary elections are held. No details were given as to when the new polls would take place.
The military chief also announced a national reconciliation committee that would include youth movements, and said the armed forces and police would deal "decisively" with any violence.
"Those in the meeting have agreed on a road map for the future that includes initial steps to achieve the building of a strong Egyptian society that is cohesive and does not exclude anyone and ends the state of tension and division," he said.
UN Secretary-General Ban Ki-moon appealed for a peaceful settlement of the crisis, saying he would personally deliver a message to the country's leaders later in the day.
He said the "voices and aspirations of the people should have been heard" and that it was important to restore the democratic process in a "very volatile" situation.
President Barack Obama voiced his concern over the military intervention and urged a speedy return to a democratically elected government.
In a statement he said: "We are deeply concerned by the decision of the Egyptian Armed Forces to remove President Morsi and suspend the Egyptian constitution.
"I now call on the Egyptian military to move quickly and responsibly to return full authority back to a democratically elected civilian government as soon as possible through an inclusive and transparent process, and to avoid any arbitrary arrests of President Morsi and his supporters."
The US and other world powers have not branded Mr Morsi's removal as a military coup - which might trigger sanctions.
British Foreign Secretary William Hague said he had talked with his Egyptian counterpart and had been reassured that "there will be early presidential elections".
He said: "It is the problem with a military intervention that it is a precedent for the future, that if this is going to happen to a democratically elected president it can happen to another in the future, and that's why it's so important to entrench democratic institutions."
The Foreign Office has advised British citizens to avoid all non-essential travel to Egypt apart from the Red Sea resorts, and to monitor travel advice from the Foreign Office.
EU foreign policy chief Catherine Ashton condemned the bloodshed and also called for a swift return to democracy.
Mr Morsi's overthrow came after days of demonstrations against the government. He rejected calls to step down and defied an army deadline.
Sky's Middle East Correspondent Sam Kiley said the atmosphere among Muslim Brotherhood supporters was "extremely subdued", with many going underground.
"One person, asking to remain anonymous, says that he feels that for them the regime has gone back to the days of Hosni Mubarak, when they were a banned organisation and their leadership was in jail."
The Brotherhood's TV station was taken off air and its managers arrested hours after Mr Morsi was overthrown.
The Egypt25 channel had been broadcasting live coverage of rallies by tens of thousands of pro-Morsi demonstrators in Cairo and around the country, with speeches by leading Muslim Brotherhood politicians denouncing the military intervention to oust the elected president.
The offices of Al Jazeera's Egyptian television channel were also reportedly raided by security forces and prevented from broadcasting from a pro-Morsi rally. Several members of staff were also reportedly detained.
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