Egypt's newly sworn-in president has vowed there will not be any reconciliation with anyone who had "committed crimes" or "adopted violence" against Egyptians, a thinly veiled reference to the Muslim Brotherhood and other Islamists.

Abdel-Fattah el-Sissi was addressing a gathering at a Cairo presidential palace late Sunday, hours after he was sworn in as Egypt's president before the Supreme constitutional Court.

The 59-year-old career soldier did not mention the Muslim Brotherhood by name or supporters of the Islamist Mohammed Morsi, the president he ousted in July after just a year in office.

Since Morsi's ouster, authorities have staged a massive crackdown against the Brotherhood and other Islamists, killing hundreds and jailing close to 20,000 others. The government has banned the Brotherhood and labelled it a terrorist organization.

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.

The building, designed to look like an ancient Egyptian temple, is a short distance away from a military hospital where ousted president Hosni Mubarak is being held.

Mideast Egypt

Abdel-Fattah el-Sissi took the oath of office before the Supreme Constitutional Court at the tribunal's headquarters in a suburb south of Cairo. (Mena/Associated Press)

Forced out of office after nearly 30 years in power by the 2011 uprising, Mubarak was convicted last month of graft and sentenced to three years in prison. He is also being retried for failing to stop the killing of hundreds of protesters during the uprising.

Sunday was declared a national holiday for el-Sissi's inauguration and police and troops were deployed throughout Cairo. The sombre ceremony was held in a red carpeted hall adorned by red, white and black Egyptian 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, around a hundred el-Sissi supporters gathered, waving Egyptian flags and posters of the country's new president. There were also army pickup trucks fitted with machine-guns and helicopters hovering overhead. El-Sissi arrived at the ceremony by helicopter.

El-Sissi has become Egypt's eighth president since the overthrow of the monarchy in 1953, the year after a military coup. With the exception of Morsi and two civilians who served in an interim capacity, all of Egypt's presidents have hailed from the armed forces.

El-Sissi won a landslide victory in presidential elections held last month, receiving nearly 97 per cent of the vote, with a turnout of 47.45 per cent.

The three-day election was declared free of fraud but was tainted by the extraordinary means used by authorities to get the vote out, including a threat to slap a fine on those who stayed home, extending the vote by an extra day, declaring the second day a national holiday and allowing free rides on trains and buses to encourage voters to travel to their home districts to cast their ballots.

Mideast Egypt US El-Sissi

The presidency of retired military chief Field Marshal Abdel-Fattah el-Sissi follows three years of upheaval in Egypt since a popular uprising ended 30 years of rule by former air force commander Hosni Mubarak. (Alexander Zemlianichenko/The Associated Press)

The election was also held against a backdrop of vastly curbed freedoms in the 11 months since Morsi's ouster and a massive crackdown on supporters of his Muslim Brotherhood, hundreds of whom have been killed in clashes with security forces.

Police state accusations

The pro-military media has meanwhile demonized not only the Brotherhood but also secular icons from the 2011 uprising.

El-Sissi's ouster of Morsi on July 3, 2013 made him an instant hero in the eyes of many Egyptians, with supporters viewing him as a strong leader who can restore stability after three years of turmoil.

But Morsi's Islamist supporters — thousands of whom have been jailed since his ouster — accuse el-Sissi of crushing Egypt's infant democracy, and many of the secular youths behind the 2011 uprising say he has revived Mubarak's police state, pointing to a law passed last year that restricts protests as well as the jailing of a number of well-known activists.

El-Sissi made it clear in a series of media interviews ahead of the May 26-28 vote that his priorities were security and the economy, maintaining that free speech must take a back seat while he fights Islamic militants waging a campaign of violence against the government and works to revive the ailing economy.

But while many in Egypt agree that the fight against militancy comes before everything else, his plans for the economy — which revolve around a strong state willing to intervene and a call for Egyptians to buckle down and work harder — have generated less enthusiasm.

Promising "great leaps," el-Sissi has advocated heavy government involvement in the economy with state-sponsored mega-projects to create jobs, going as far as to say the government should set prices for some goods. At the same time, he has vowed to be business-friendly and encourage investment.

He has spoken of reshaping the map of Egypt by expanding Nile provinces into the desert to make way for development outside the densely populated river valley. His answer for funding his projects is billions of dollars from oil-rich Gulf nations and Egyptian expatriates.