The top judge of Egypt?s Constitutional Court, Adly Mahmud Mansour, has been sworn in as interim leader, hours after the army ousted President Mohammed Morsi and put him under house arrest.
Mr Mansour praised the armed forces and the Egyptian people, saying the era of ?worship of the ruler? should end.
Mr Morsi, Egypt?s first freely elected leader, is under house arrest after what he says was a military coup.
The army said he had ?failed to meet the demands of the people?.
The upheaval comes after days of mass rallies against the Islamist president.
Protesters accused Mr Morsi and the Muslim Brotherhood of pursuing an Islamist agenda for the country and of failing to tackle Egypt?s economic problems.
Some 50 people have died since the latest unrest began on Sunday.
Mr Mansour was appointed chief justice of the Supreme Constitutional Court only four days ago, and was sworn in to that office on Thursday morning, before being sworn in as interim head of state.
?I swear to preserve the system of the republic, and respect the constitution and law, and guard the people?s interests,? he said.
The time had come to ?stop our industry of making tyrants?, he said, and new elections were ?the only way for a brighter future?.
The audience repeatedly applauded as Mr Mansour praised the military as ?the conscience of the nation and the guarantor of its security and safety?.
He also hailed the police, the media, and the judiciary, and urged the Egyptian people to continue their protests.
US concern
Mr Morsi?s opponents celebrated through the night in Cairo?s Tahrir Square, after the army announced it had suspended the Islamist-backed constitution ? approved by a referendum in 2012 ? and pledged to hold new elections.
But a number of people were killed as clashes erupted overnight between Morsi supporters and the security forces in Cairo and Alexandria.
Gehad el-Haddad, a spokesman for Mr Morsi?s Muslim Brotherhood, told the BBC the ousted leader had been put under house arrest and the ?entire presidential team? was in detention.
Mr Haddad?s father, senior Morsi aide Essam el-Haddad, and Saad al-Katatni, head of the Brotherhood?s political wing, are among those held.
The state-run al-Ahram newspaper reported that arrest warrants had been issued for 300 leaders and members of the Muslim Brotherhood.
US President Barack Obama has said he is ?deeply concerned? by the latest turn of events and called for a swift return to civilian rule.
The removal of the president followed four days of mass protests against Mr Morsi and an ultimatum issued by the military, which expired on Wednesday afternoon.
In his televised speech, Gen Sisi said the armed forces could not ignore the call of the Egyptian masses.
He spoke of a new roadmap for the future, and said Mr Mansour would be given the task of ?running the country?s affairs during the transitional period until the election of a new president?.
The army?s roadmap for the post-Morsi era includes:
Suspension of the constitutionA civilian, transitional technocratic governmentSupreme Constitutional Court to prepare for presidential and parliamentary electionsA ?charter of honour? to be drawn up and followed by national media
BBC
