Last Updated 2:55 p.m. ET
(CBS/AP) CAIRO - Defying the nation's military rulers, Egypt's newly elected president read a symbolic oath of office Friday in Tahrir Square - the main stage in the uprising that overthrew President Hosni Mubarak - and told the crowd of thousands in attendance that he feared "no one but God."
Mohammed Morsi of the Muslim Brotherhood - the first Islamist and first civilian to win the presidency - made his first public speech since being declared the winner of the nation's presidential runoff election, as he faces a power struggle with the country's ruling generals who are trying to limit presidential authority in a post-Mubarak country.
His visit to Tahrir is also a nod to the protesters who supported his bid for leadership in a bitter campaign that pitted him against Mubarak's last prime minister Ahmed Shafiq.
Telling the crowd that the revolution will continue, the president-elect vowed that the power of the people is above all and that no one can take away the president's authorities.
But he is already facing a serious challenge after the Mubarak-era military rulers who oversee the transition took a series of decisions undermining the powers of his office before his swearing-in, which was scheduled for Saturday.
Many protesters have called for Morsi to take the oath of office in the square, the epicenter of mass protests against Mubarak and later the continued military rule, but the ceremony was scheduled to be held Saturday before a high court.
His appearance in Tahrir a day before the official ceremony is clearly a nod to the calls for a popular oath.
In his speech following Friday prayers, Morsi promised to free detained Egyptian protesters facing military tribunals.
Morsi also vowed to free the blind sheik Omar Abdel-Rahman, the spiritual leader of those convicted in the 1993 World Trade Center bombing, who is jailed in the U.S. for a plot to blow up New York City landmarks.
Egyptians will be watching Morsi's statements to see whether he will accept the restrictions on his power or try to use his position as an elected president to force the military to lift them. His influence is hampered by a court decision that dissolved the country's first freely elected parliament, which was dominated by Islamists.
The ruling generals have promised to transfer power to an elected president by Sunday. But they also have given themselves sweeping powers that undercut the authority of the president. The constitutional declaration -- issued days before the winner of a runoff vote was announced -- also designated the generals the country's legislature in place of the disbanded parliament.
Protesters -- mainly Islamists but also including some of the liberal and secular activists who spearheaded the revolution against Mubarak -- took to the streets to demand that the generals rescind the declaration and reinstate the parliament.
Morsi's spokesman, Yasser Ali, said the president-elect wants to stand with the thousands who have camped in the square for over a week to express concern about the power grabs.
"He wants to confirm that people are the source of his power," Ali said. "He wants to show unity with his people over issues of the transition, which is now ending."