Egyptians have ransacked the Cairo headquarters of President Mohamed Morsi's Muslim Brotherhood after massive protests took a violent turn.
Protesters stormed the building early Monday, smashing windows and tossing firebombs even as guards inside the building fired back. Some protesters were seen running off with furniture and files.
Activists say at least five people were killed in the incident, while Egyptian officials say the nationwide death toll since Sunday has risen to 16.
Opposition organizers have given President Morsi until 5 p.m. Cairo time Tuesday to resign.
Sunday's anti-government demonstrations in Egypt were the largest since the 2011 revolution that swept former president Hosni Mubarak from power. Arabic-language media quoted the Interior Ministry saying the crowds in Cairo and other cities across Egypt totaled as many as 3 million people.
Some protesters remained in Cairo's Tahrir Square overnight and some, like Jamal Helal, vowed not to back down.
SOUNDBITE: (Arabic) Jamal Helal, anti-Morsi protester // from Egypt Tension 2- 898615 ))
"Don't you (Morsi) see that the country is sinking? You should understand that. You also should understand that people don't want you any more. Be fair."
As tensions mounted Sunday, the presidential office issued a statement saying dialogue is the only way out of Egypt's political crisis.
In an interview published in the British newspaper The Guardian, President Morsi said that if he gave in to the pressure, a new president could face similar opposition demands to quit after a "week or a month."
Egypt's military has warned both sides to resolve their differences through negotiations but neither the military nor the police intervened when protesters stormed the Muslim Brotherhood headquarters in Cairo.
Since last week, supporters and opponents of President Morsi have been engaging in sporadic and sometimes deadly clashes.