More Cairo clashes after Port Said football deaths
At least four people have been killed in the latest unrest in Egypt, amid anger over 74 deaths after a football match in Port Said on Wednesday.
Many Egyptians blame the authorities for failing to protect fans.
Egypt's military rulers issued a statement calling for the country to unite and return to stability.
A building opposite the ministry which houses the property tax authority was set on fire, state TV reported.
A demonstrator and a soldier died on Friday in the clashes in Cairo as police fired tear gas at stone-throwing crowds. At least two people were also killed in Suez.
Ambulances and motorcycles ferried many of the injured to field hospitals.
The health ministry said 1,051 people were injured on Friday, the AFP news agency reported.
In its statement, the Supreme Council of the Armed Forces (Scaf) said Egypt was passing through "the most dangerous and most important phase in Egypt's history".
Revenge for revolution?
The latest bout of unrest began on Wednesday, after a pitch invasion in Port Said, when Cairo's visiting al-Ahly side were attacked after losing to the local al-Masry side. Seventy-four people died and more than 1,000 were injured.
Most of the dead were believed to be al-Ahly supporters. Hardcore fans - known as "ultras" - have accused the authorities of allowing the killings to happen.
They say the authorities wanted revenge because the ultras were among those battling the police during last year's revolution that ousted strongman leader Hosni Mubarak.
Anger over the deaths has combined with widespread frustration at the pace of reforms undertaken by Egypt's interim military rulers.
On Thursday, about 10,000 protesters clashed with police outside the interior ministry in Cairo. More than 1,000 were injured, the health ministry said.
Some 54 police officers and soldiers were also reported hurt.
By Thursday night, the unrest had spread across the country. Two people were shot dead in Suez as a crowd of hundreds attempted to overrun a police station.
On Friday, protests resumed outside the interior ministry, where at least one protester was reported dead. A soldier also died from injuries sustained on Thursday, state media said.
The demonstrators say they do not want to storm the ministry, but to hold a sit-in in front of it, the Associated Press reports.
One of the demonstrators, who gave his name as Ahmed, told the BBC: "We need to remain peaceful, and right now we can't.
"If people go to the interior ministry, they are attacked by security forces. The protesters are peaceful; they aren't attacking anyone, but we can't win like this," he said.
In Alexandria, a protest march headed for the regional offices of the military government.
Protester Wael Nawara told the BBC's Network Africa programme that many middle-ranking officers loyal to the former president were still in charge at the ministry and were "conspiring against revolution".
"There have been many calls throughout the last few months of restructuring the ministry of interior to bring the officers who are responsible for earlier deaths to trial, but nothing really has changed much in the behaviour of the ministry," he said.
The government has dismissed several senior officials in response to the football deaths.
Port Said's director of security and the head of investigations were suspended and are now in custody.