Protesters and riot police fought pitched battles in Cairo on Sunday as clashes sparked by the failure of Egypt's military rulers to prevent deadly football-linked violence raged into a fourth day.
Hundreds of riot police blocked off roads leading to the interior ministry headquarters in the centre of the capital, firing tear gas to keep dozens of rock throwing protesters at bay.
Police erected a concrete block wall on Mansur street, which has become the nerve centre of the deadly clashes, while entrenching themselves behind coils of barbed wire on other roads.
Protesters lobbing stones and petrol bombs at the police lines cheered when their comrades brought back a captured man they said was a plainclothes officer. Others tried to shield him from the protesters' kicks and punches.
The protesters denied they intended to storm the ministry, several hundred metres (yards) from Tahrir Square, the epicentre of the uprising that overthrew president Hosni Mubarak a year ago but left the military in charge.
"My heart burned at what happened in Port Said, and we all know that the police are responsible," said one of the protesters, a high school student who gave his name as Ahmed Farag.
"We don't want to storm the ministry. We are protesting here because this is the police headquarters."
The health ministry on Saturday said 12 people have been killed in Cairo and the town of Suez since the violence erupted on Thursday in response to the failure of authorities to contain clashes at a football match in the northern city of Port Said that left 74 people dead.
Marchers took to the streets nationwide Friday to demand Egypt's ruling generals cede power immediately, amid charges the military was deliberately sowing chaos to justify its status at the top of the political ladder.
Many of the dead in the football riot in Port Said were thought to have been Ultras -- supporters of Cairo's main club Al-Ahly -- set upon by partisans of the local Al-Masry side after the Cairo team lost 3-1.
The Ultras played a prominent role in the uprising that overthrew Mubarak, and commentators have fed speculation that pro-Mubarak forces were behind the massacre, or at least complicit in it.
The military has pledged to cede full powers to civilian rule when a president is elected by the end of June, but its opponents believe it intends to hold on to power behind the scenes after a transfer to civilian rule.