Egypt protesters storm Muslim Brotherhood headquarters
Anti-government protesters in Egypt have stormed the national headquarters of President Mohammed Morsi's Muslim Brotherhood in the capital, Cairo.
People ransacked the building in the Moqattam area and set parts on fire.
Officials say eight people have been killed in clashes outside since Sunday, while eight others have died elsewhere.
Meanwhile, four ministers are reported to have resigned, a day after millions took to the streets across the country to demand the president leave power.
The al-Watan website said the ministers of tourism, environment, communication and legal affairs had acted "in solidarity with the people's demand to overthrow the regime".
On Monday afternoon, Egyptian state television reported the armed forces would issue a statement on the situation later in the day, but did not provide further details.
Earlier, the opposition movement behind the protests, Tamarod (Revolt), gave Mr Morsi until Tuesday afternoon to step down and call fresh presidential elections, or else face a campaign of civil disobedience.
Protesters across Egypt accuse the president of failing to tackle economic and security problems since being elected a year ago. His supporters insist he needs more time.
The crowds seen in Cairo's Tahrir Square on Sunday were the biggest since the 2011 revolution that toppled Hosni Mubarak.
Protests and sporadic outbreaks of violence were reported nationwide.
The health ministry said at least 16 people had been killed and 781 injured since Sunday.
Three people died in the central province of Assiut, and another four in Alexandria, Fayoum, Beni Suef and Kafr al-Sheikh. Another protester suffocated to death at a protest outside the Ittihadiya presidential palace in Cairo.
Eight people were killed in clashes around the Muslim Brotherhood's headquarters in Moqattam, the ministry added.
Overnight, protesters threw petrol bombs and rocks at armed guards inside the six-storey building, who retaliated by firing at them.
On Monday morning, the protesters stormed the headquarters and began throwing objects out of broken windows. One protester was seen removing parts of the signage, while another waved an Egyptian flag from a window. Later, people began walking out carrying office equipment.
"This is a historic moment. The Brotherhood ruined the country, so stealing from them is justified," one man, named Mohammed, told the AFP news agency.
Many protesters accuse the president of putting the Brotherhood's interests ahead of the country's as a whole.
Brotherhood spokesman Gehad El-Haddad criticised the security forces for failing to protect the building and warned that the movement was considering action to defend itself.
"It's very dangerous for one entity in society to take up violence as a means of change because it may entice others to do so," he told the Reuters news agency.
Mr Haddad noted that self-defence committees had been set up during the 2011 uprising, and said the Brotherhood's Guidance Bureau would make an announcement later on Monday.
"The people will not sit silent," he added.
Some protesters had spent the night camped out in Tahrir Square and also in front of the Ittihadiya presidential palace to the north-east. They vowed to stay there until the president stepped down.
One man heading to the palace was confident it would not take long.
"Mubarak took only 18 days although he had behind him the security, intelligence and a large sector of Egyptians," Amr Tawfeeq told the Associated Press.
Earlier, Tamarod issued a statement saying the protesters would give Mr Morsi until 17:00 (15:00 GMT) on Tuesday to leave power and allow state institutions to prepare for early presidential elections.
Otherwise, people would begin a campaign of "complete civil disobedience", the group warned.
It urged "state institutions including the army, the police and the judiciary, to clearly side with the popular will as represented by the crowds".
The group also rejected offers of dialogue from the president.
"There is no way to accept any half measures," it said. "There is no alternative other than the peaceful end of power of the Muslim Brotherhood and its representative, Mohammed Morsi."
On Saturday, Tamarod said it had collected more than 22 million signatures - more than a quarter of Egypt's population - in support.
But Mr Morsi was defiant in an interview published on Sunday, rejecting the opposition calls for early presidential elections.
"If we changed someone in office who [was elected] according to constitutional legitimacy - well, there will be people opposing the new president too, and a week or a month later they will ask him to step down," he told the Guardian newspaper.
"There is no room for any talk against this constitutional legitimacy. There can be demonstrations and people expressing their opinions. But what's critical in all this is the adoption and application of the constitution."