(CNN) -- Egypt's former military chief Abdel Fattah el-Sisi was sworn in Sunday as President, vowing to lead the country through important changes.
In its next phase, Egypt "will witness a total rise on both internal and external fronts, to compensate what we have missed and correct the mistakes of the past," he said.
Despite the political upheaval Egypt has faced in recent years, el-Sisi celebrated the transition from interim President Adly Mansour. "In the long history that goes back thousands of years, our homeland did not witness democratic transfer of power. Now, for the first time, the President-elect shakes hands with the outgoing President, and together they sign a power transfer document in an unprecedented occasion," he said in an address in front of the Supreme Constitutional Court's General Assembly in Cairo.
El-Sisi won 96% of the vote in last month's presidential election for a four-year term. When he was declared the winner last week, a boisterous celebration erupted in Cairo's Tahrir Square, filled with fireworks and balloons bearing his image. Military and security personnel watched from the edges as crowds danced and sang.
Washington is looking forward to working with el-Sisi "to advance our strategic partnership and the many interests shared by the United States and Egypt," the White House press secretary said last week.
The election was called amid political turbulence that saw Mohamed Morsy -- the country's first democratically elected President after the ouster of longtime leader Hosni Mubarak -- removed from power in a July military coup.
El-Sisi, who was army chief at the time, stepped down from his military post this year to run for President.
The White House said while it is pleased that international observers were allowed to participate in the election, "we also share concerns raised by observation groups about the restrictive political environment in which this election took place."
"As Egypt looks toward parliamentary elections later this year, we urge the government to consider the recommendations of the observer groups on ways to improve the administration of future elections," the White House said.
El-Sisi's sole opponent, Hamdeen Sabahy, received 3.9% of the vote, the country's election commission said. Sabahy conceded defeat but raised questions about the political process.
Allegations were made that Sabahy campaign representatives were attacked and detained, and that el-Sisi's representatives were allowed inside polling stations, Egypt's state-run Ahram Online news agency has reported.
"We cannot give any credibility or ratification to the announced numbers of turnout or results," Sabahy said last month. "The announced results are an insult to the intelligence of the Egyptians."