EGYPT'S new president moved to assert his authority and regain control of the streets Saturday even as his Islamist opponents declared his powers illegitimate and issued blood oaths to reinstate Mohammed Morsi, whose ouster by the military has led to dueling protests and deadly street battles between rival sides.

But underscoring the sharp divisions facing the untested leader, Adly Mansour, his office said pro-reform leader Mohamed ElBaradei had been named as interim prime minister but later backtracked on the decision saying consultations were continuing. A politician close to ElBaradei said the reversal was due to objections by an ultraconservative Islamist party with which the new administration wants to cooperate.

Mansour's administration, meanwhile, has begun trying to dismantle Morsi's legacy. He fired Morsi's intelligence chief and the presidential palace's chief of staff. Prosecutors, meanwhile, ordered four detained stalwarts of Morsi's Muslim Brotherhood held for 15 days pending an investigation into the shooting deaths of eight protesters last week.

No major violence was reported between supporters and opponents of Morsi as the two sides sought to regroup after a night of fierce clashes that turned downtown Cairo into a battlefield. Clashes were also fierce in the port city of Alexandria, where thousands from both sides fought each other with automatic rifles, firebombs and clubs.

Friday's violence left 36 dead, taking to at least 75 the number of people killed since the unrest began on June 30, when millions of protesters took to the streets on the anniversary of Morsi's inauguration as Egypt's first democratically elected president.

Morsi, a U.S.-trained engineer who was widely accused by critics of monopolizing power for himself and the Brotherhood as well as his failure to implement democratic and economic reforms, remained under detention in an undisclosed location.

Tensions were still high as tens of thousands of Morsi supporters rallied for a third day near a mosque in a Cairo neighborhood that has traditionally been a stronghold of Islamists, chanting angry slogans against what they called a coup by Gen. Abdel-Fattah el-Sissi. The general has denied the military staged a coup, saying he was acting on the wishes of millions of Egyptians protesting the ex-Islamist leader.

"El-Sissi is a traitor," declared an English language banner bearing an image of the army's chief and hoisted by Morsi's supporters.

Setting up another showdown, the youth opposition group behind the series of mass protests that led to Morsi's ouster called on Egyptians to take to the streets on Sunday to show support for the new order.

Mansour, 67, the former chief justice of the country's Supreme Constitutional Court who was installed by the military as an interim leader, is little-known in international circles and the choice of ElBaradei would have given his administration a prominent global face to make its case to Washington and other Western allies trying to reassess policies.

But news of ElBaradei's appointment, which was reported by the state news agency MENA and others, proved divisive.

The 71-year-old Nobel laureate was an inspiring figure to the youth groups behind the 2011 revolution that toppled autocrat Hosni Mubarak as well as the uprising against Morsi. His appointment as prime minister would cement Mansour's support among the young anti-Morsi protesters.

But a senior opposition official close to ElBaradei, Munir Fakhry Abdelnur, told The Associated Press that the last minute reversal was because the ultraconservative Salafi el-Nour party was opposed.

Mansour's spokesman Ahmed el-Musalamani denied that the appointment of the former U.N. nuclear negotiator was ever certain. However, reporters gathered at the presidential palace ahead of his news conference were told earlier that the president would arrive shortly to announce it.

The dispute over ElBaradei underlines the fragmentation of Egypt's politics as the country continues to be roiled by bout after bout of unrest and violence since Mubarak's ouster.

The 2011 uprising opened the way for the political rise of the Muslim Brotherhood, which was long suppressed by Mubarak's Western-backed regime, and Morsi was elected last year by a narrow margin. The fundamentalist movement swiftly rejected ElBaradei's appointment.

The Brotherhood has vowed to boycott the political process, saying the military maneuver was a coup that overturned a democratically elected government.

"Now it's clear that the Mubarak regime has the upper hand," Brotherhood spokesman Ahmed Aref alleged. "We cannot accept the strategy of arm twisting; we cannot accept the authority being snatched by force," he told The AP.

The group's powerful deputy Khairat el-Shater, former leader Mahdi Akef, Rashad Bayoumi and Saad el-Ketatni have been accused of inciting violence against protesters in Cairo.

The silver-haired new president, meanwhile, insisted national reconciliation was his top priority.

"Enough already with divisions," he told reporters. "We need to mobilize our forces to build this nation," he said. He also called on the Brotherhood to join the political process. "The Brotherhood is a part of this nation, if they decide to join, we will welcome them."

"I want everyone to pray for me. Your prayers are what I need from you," he told worshippers on Friday in comments published Saturday by the independent el-Tahrir daily.

On Saturday, he met with el-Sissi and Interior Minister Mohammed Ibrahim, who is in charge of the police. Later he met with the three young leaders of Tamarod, or Rebel, which organized the massive opposition protests that began June 30.

Despite his words, both sides braced for the possibility of more violence as Egypt's political unraveling increasingly left little room for middle ground or dialogue.

In the northern part of the Sinai Peninsula, gunmen shot dead a Christian priest while he shopped for food in an outdoor market on Saturday. It was not immediately clear if the shooting was linked to the political crisis, but minority Christians have faced increased attacks in the wake of the Islamist rise to power in the nation of 90 million people.

In Cairo's eastern suburb of Nasr City near the Rabaah al-Adawaiya mosque - the main rallying Muslim Brotherhood rallying point - lines of fighters brandished homemade weapons and body armor at road blocks decorated with Morsi's picture.

"The people here and in all of Egypt's squares are ready for martyrdom to restore legitimacy," said Abdullah Shehatah, a senior leader of the Freedom and Justice Party, the Brotherhood's political arm. "This coup and all its institutions are illegal."

Next door in the relatively upscale Heliopolis district, people chanted against Morsi and honked car horns in appreciation of roadblocks manned by Egypt's military.

Security forces boosted their presence with armored personnel carriers and checkpoints across the nation's capital.

By nightfall, however, the number of Morsi supporters swelled with people hoisting Morsi posters and, at one point, chanting in English for the benefit of the foreign media. "Free Egypt," they chanted. Smaller crowds gathered elsewhere in Cairo, including about 2,000 outside the headquarters of the Republican Guard, where Morsi was first confined by the military before he was taken to an undisclosed Defense Ministry facility.

Soldiers in full combat gear watched from behind razor wire.

A Cairo court, meanwhile, adjourned to Aug. 17 the retrial of Mubarak over charges of corruption and involvement in the killing of protesters during the 2011 uprising that ousted him. Mubarak and his two sons, Alaa and Gamal, who are on trial for corruption, appeared at the court session on Saturday.

Originally published as ElBaradai's appointment 'not certain'