Egypt's president holds crisis talks with security officials, names opposition leader interim prime minister Egypt's new president moved to assert his authority Saturday by naming a chief rival of ousted leader Mohammed Morsi as interim prime minister and holding crisis talks with security officials on efforts to reclaim control of the streets, Fox News confirms. The steps by Adly Mansour are likely to deepen the defiance by Islamist opponents who have turned parts of Cairo into vigilante-guarded strongholds and have issued blood oaths to battle until Morsi is restored. After a night of clashes that claimed at least 36 lives and injured more than 200, both sides appeared to be preparing for the possibility of more violence as Egypt's political unraveling increasingly left little room for middle ground or dialogue. Only a fraction of Cairo's normally heavy traffic was on the streets amid worries that violence could flare up again. Security forces stepped up their presence near the largest concentration of Morsi supporters on the streets: A sit-in outside a mosque in Cairo's eastern Nasr City district, a traditionally Muslim Brotherhood stronghold. In Nasr City lines of fighters brandished homemade weapons and body armor at road blocks affixed with Morsi's picture. 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 -- whose snub of Morsi's authority earlier this week tipped the scales against Egypt's first elected leader. Mansour's decision to bring pro-reform leader and Nobel laureate Mohamed ElBaradei into the key government role of prime minister is also certain to help cement the loyalties of the anti-Morsi forces. The president planned to swear-in ElBaradei later Saturday, an assistant to ElBaradei confirmed to Fox News. ElBaradei, a former director of the U.N.'s nuclear watchdog agency, led the protests against President Hosni Mubarak during the Arab Spring uprising that ended his autocratic rule in February 2011. The revolution also opened the way for the political rise of the Muslim Brotherhood, which was long under pressure from Mubarak's Western-backed regime. Elections last year brought Morsi to the presidency, but ElBaradei remained a voice of dissent, once saying the Brotherhood lived "in a delusion" for thinking its members could manage the country on their own. The choice of the 71-year-old ElBaradei gives the administration and prominent global figure a chance to make its case to Washington and other Western allies trying to reassess policies after what Morsi's backers have described as a "coup." Morsi remains under detention in an undisclosed location. In a further sign of the concern the unrest could spin out of control, Mansour, held talks with the army chief and Defense Minister Gen. Abdel Fattah el-Sissi as well as Interior Minister Mohammed Ibrahim. It was the first time Mansour has worked out of the president's main offices since he was sworn-in Thursday as the country's interim leader. Mansour also met with leaders of Tamrod, or Rebel, the youth movement that organized the mass anti-Morsi demonstrations, according to the officials who spoke on condition of anonymity. Gunmen shot dead a Christian priest Saturday while he shopped for food in an outdoor market in the northern Sinai Peninsula Saturday. It was not immediately clear if the shooting was linked to the political crisis, but there has been a backlash against Christians since just before and after Morsi's ouster. Attacks have occurred on members of the minority by Islamists in at least three provinces south of Egypt. Morsi's Brotherhood and hard-line allies claim the Christians played a big part in inciting against the ousted leader. Officials have briefly detained top figures from Morsi's Muslim Brotherhood and have kept him from the public eye, under detention in an undisclosed location. Morsi's supporters have vowed to take to the streets until he is reinstated. His opponents, meanwhile, have called for more mass rallies to defend what they call the "gains of June 30," a reference to the start of massive protests to call for the ouster of the president. There were no reports of major clashes after dawn Saturday, following a night of street battles that added to an overall death toll of at least 75 in the past week. The Interior Ministry reported that at least eight policemen have been killed since June 30. The Health Ministry official's deputy, Khairat el-Shater, considered the most powerful figure in the organization, was arrested in a Cairo apartment along with his brother on allegations of inciting violence, Interior Ministry spokesman Hani Abdel-Latif told The Associated Press. Egyptian troops reportedly opened fire on Morsi supporters Friday outside Republican Guard headquarters near Cairo, where Morsi was believed held. There were initially conflicting reports on casualties, but an army spokesman denied troops shot at Morsi supporters, saying only blanks and teargas were used. Crowds of Islamists gathered to cross a bridge over the Nile River after nightfall and clashed with Morsi opponents near Tahrir Square and outside the state TV building. Badie, who was taken into custody shortly after Morsi was ousted, addressed the military, saying it was a matter of honor for it to abide by its pledge of loyalty to the president, in what appeared to be an attempt to pull it away from its leadership that removed Morsi. Fox News' Greg Palkot, The Associated Press and Reuters contributed to this report.