CAIRO — Egypt's new president moved to assert his authority on Saturday by naming a chief rival of ousted leader Mohamed Morsi as interim prime minister and holding crisis talks with security officials on efforts to reclaim control of the streets. The steps by the untested Adly Mansour, however, are likely to deepen the defiance by Islamist opponents who have turned parts of the 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, 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. 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. ElBaradei, a former director of the UN's nuclear watchdog agency, led the protests against president Hosni Mubarak during the Arab Spring uprising. Egypt's new president — chief justice of the country's constitutional court — is little-known in international circles. But the choice of the 71-year-old ElBaradei gives the administration and prominent global figure 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. Earlier, the president held talks with the army chief and interior minister in apparent attempts to work out strategies to contain another round of violence. Morsi's supporters have vowed to take to the streets until the toppled Islamist leader is reinstated. His opponents, meanwhile, have called for more mass rallies to defend what they call the “gains of June 30.” “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. Speaking at the main sit-in site of Morsi supporters in Cairo, he said: “This coup and all its institutions are illegal.” – AP