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 restore Mohammed Morsi, whose ouster by the military has led to dueling protests and pitched street battles between rival sides.

But underscoring the sharp divisions facing the untested leader, Adly Mansour, his office said it was naming Mohammed ElBaradei, one of Morsi's top critics, as interim prime minister but later backtracked on the decision.

Mansour's spokesman Ahmed el-Musalamani denied that the appointment of the Nobel Peace laureate was ever certain. However, reporters gathered at the presidential palace were ushered into a room where they were told by an official to wait for the president who would arrive shortly to announce ElBaradei's appointment.

A senior opposition official, Munir Fakhry Abdelnur, told The Associated Press that the reversal was because the ultraconservative Salafi el-Nour party objected to ElBaradei's appointment and mediation was underway.

Tensions were 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 Wednesday's toppling of the country's first democratically elected president 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.

Mansour, 67, the former chief justice of the country's constitutional court who was installed by the military as an interim leader, met earlier Saturday with el-Sissi and Interior Minister Mohammed Ibrahim, who is in charge of the police. He also met separately with the three young leaders of Tamarod, or Rebel, which organized the massive opposition protests that began June 30, the anniversary of Morsi's inauguration.

Morsi's Muslim Brotherhood, meanwhile, has promised 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."

The new president, meanwhile, insisted national reconciliation was his top priority. "We all need national reconciliation and we will work to realize it," he was quoted as saying in a brief interview with the independent el-Tahrir daily. "Egypt is for everyone."

"I want everyone to pray for me. Your prayers are what I need from you," he told worshippers on Friday who approached to shake his hand and wish him well, according to el-Tahrir.