Former army chief Abdel Fattah al-Sisi takes the oath of office during his swearing-in ceremony as Egypt's new president at the Supreme Constitutional Court in Cairo, June 8, 2014 in this still image taken from video.[Photo/Agencies]

CAIRO - Egypt's former army chief Abdel-Fattah el-Sissi was sworn in on Sunday as president for a four-year term, taking the reins of power in a nation roiled since 2011 by deadly unrest and economic woes.

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El-Sissi's inauguration came less than a year after the 59-year-old career infantry officer ousted the country's first freely elected president, the Islamist Mohammed Morsi, following days of mass protests by Egyptians demanding he step down.

El-Sissi took the oath of office before the Supreme Constitutional Court at the tribunal's Nile-side headquarters in a suburb south of Cairo, the same venue where Morsi, now on trial for charges that carry the death penalty, was sworn in two years ago.

Sunday was declared a national holiday and tight security was enforced by the police and military throughout Cairo.

The somber ceremony was held at a red carpeted hall adorned by Egypt's red, white and black flags and attended by the entire Cabinet of Prime Minister Ibrahim Mahlab as well as el-Sissi's wife and children.

El-Sissi entered the hall walking side by side with the outgoing interim president Adly Mansour, who will now return to his post as chief justice of the Supreme Constitutional Court after nearly a year in office.

Outside the building, modelled to look like an ancient Egyptian temple, around a hundred el-Sissi supporters gathered, waving Egyptian flags and posters of the country's new president.