In his first address to the nation on Thursday, Adly Mahmud Mansour promised to guard people’s interest as he took the oath of office at a ceremony in the Supreme Constitutional Court building in the capital, Cairo.

Late Wednesday, General Abdel Fattah al-Sisi, the head of Egypt’s army, announced that Morsi was no longer in office during a speech on state television.

Sisi said Morsi, who was Egypt’s first freely elected president, had “failed to meet the demands of the people.”

“I swear to preserve the system of the republic, and respect the constitution and law, and guard the people’s interests,” Mansour said.

During his speech, army-mandated Mansour hailed the military and police in dealing with the political crisis facing the country.

Mansour vowed to lead a “modern, constitutional, national and civil country.”

He went on to say that the Muslim Brotherhood is a “part of the nation” and invited the party to “share in building the country.”

Having served as deputy head of the Supreme Constitutional Court since 1992, Mansour was named chief of the court in May 2013 and took up his post on July 1.

Mansour also suspended the country’s constitution, saying that new parliamentary elections will be held.

Following the speech by Sisi, police began arresting key presidential aides and the leaders of the Muslim Brotherhood.

Morsi’s ouster came after days of massive anti-government protests across the country.

A senior Egyptian army official said on Thursday that Morsi is being held “preventively” by the military.

“He (Morsi) is being held preventively for final preparations,” said the army official, whose name was not mentioned in the reports.

Morsi might face formal charges over accusations made by his opponents, the official stated.