At least 16 people died in protests across Egypt on Sunday, including eight in clashes between opponents and supporters of President Mohamed Morsi in Cairo, the health ministry said on Monday.
A further three people died in the central province of Assiut and one in each of the provinces of Fayoum, Beni Sueif and Kafr el-Sheikh.
One protester suffocated to death at the rally outside the presidential palace in Cairo and another died of wounds in the coastal city of Alexandria, the ministry said.
Egypt’s opposition Monday gave Islamist Mohamed Morsi a day to quit or face civil disobedience after deadly protests demanded the country’s first democratically elected president step down after just a year in office.
“We give Mohamed Morsi until 5:00pm (1500 GMT) on Tuesday July 2 to leave power, allowing state institutions to prepare for early presidential elections,” the Tamarod movement said in a statement on its website.
Otherwise, “Tuesday, 5:00 pm will be the beginning of a complete civil disobedience campaign.”
In Cairo, the seat of the powerful Muslim Brotherhood from which Morsi hails was set ablaze before people stormed and looted it, an AFP correspondent said.
People were seen leaving with petrol bombs, helmets, flak jackets, furniture, televisions and documents.
“This is a historic moment. The Brotherhood ruined the country, so stealing from them is justified,” protester Mohammed told AFP.
Tamarod – Arabic for Rebellion – is a grassroots campaign which says it collected more than 22 million signatures declaring a lack of confidence in Morsi.
It was behind Sunday’s protests that saw millions of people pour onto the streets demanding his departure on the first anniversary of his inauguration.
As Morsi stood firm and insisted the only way forward was dialogue, calls for army intervention increased.
Tamarod urged state institutions to support the protesters, calling on “the army, the police and the judiciary to clearly side with the popular will as represented by the crowds”.
Opposition leader Hamdeen Sabbahi urged military intervention if Morsi refused to quit.
The army, which led a tumultuous transition after Mubarak, had already warned it would intervene if there was major unrest.
“The armed forces must act, because they have always been on the side of the people” which “has expressed its will”, said Sabbahi, who was third in the 2012 presidential election.
The best outcome would be for Morsi to go willingly, he added.
But Morsi’s spokesman Ehab Fahmy told reporters: “Dialogue is the only way through which we can reach an understanding... The presidency is open to a real and serious national dialogue.”
Television pictures showed the Muslim Brotherhood building in Cairo burning as people pelted it with petrol bombs.
Brotherhood supporters fired buckshot in a bid to repel the attackers, an AFP journalist said. Later, automatic weapons fire was heard.
In Tahrir Square, where hundreds of protesters spent the night, demonstrators blew whistles and chanted anti-Morsi slogans around tents.
Outside the presidential palace, hundreds of others staged a sit-in after the army estimated that millions had heeded the opposition call to protest.
Sunday’s turnout – on the first anniversary of Morsi’s inauguration – was described as the largest protest in Egyptian history.
“Long live the people,” read Monday’s headline in the independent daily al-Tahrir, while Al-Masry al-Youm called it the “June 30 revolution”.
Anti-Morsi protests were held in the coastal city of Alexandria, the Nile Delta cities of Mansura, Menuf, Tanta and Mahalla, the canal cities of Suez and Port Said and the president’s hometown Zagazig.
Morsi, previously a senior Brotherhood leader, is Egypt’s first freely elected president, catapulted to power by the uprising that ended three decades of Mubarak rule.
His opponents accuse him of betraying the revolution by concentrating power in Islamist hands and of sending the economy into freefall.
Morsi supporters say he inherited many problems from a corrupt regime, and that he should be allowed to complete term which ends in 2016.
Any attempt to remove him would be a coup against democracy, they say.