Police were reported on Wednesday to have fired so many tear gas canisters at hundreds of stone and firebomb-throwing youth in the Egyptian capital that a perpetual cloud hung over the site of the ongoing clashes.
The violence exploded late Tuesday after families of some of the 850 people killed in the popular uprising that ousted President Hosni Mubarak in February held a sit-in in a Cairo suburb late on Tuesday protesting the slow prosecution of police officers who participated in Mubarak's brutal crackdown.
Egypt's interim junta claims other bereaved relatives arrived to complain that names of their own dead were not mentioned at the ceremony, sparking clashes that gravitated to the capital's central Tahrir Square and the Interior Ministry, which forced police to intervene.
Protesters, however, say it was only after police moved in and broke up the peaceful sit-in that violence erupted.
It was the first such violence in weeks in Tahrir Square, the epicenter of the revolt that toppled Mubarak on February 11. Some 1,036 people were injured, among them at least 40 policemen, according to medical officials.
Most were said to have suffered inhalation injuries, burns, and contusions from rocks and clubs.
Early in the morning young men, many stripped to the waist, were still hurling stones at police near the ministry as commuters passed by on their way to work.
Some ordinary Egyptians said those involved were bent on battling police rather than protesting. To others, the violence seemed politically motivated.
"The people are angry that the court cases against top [Mubarak] officials keep getting delayed," Ahmad Abdul Hamid, 26, a bakery employee who stayed in Tahrir Square overnight, told Reuters.
By early afternoon, eight ambulances were in Tahrir and the police had been ordered out of the square by senior commanders. Dozens of young men blocked traffic from entering the square, using stones and scrap metal.
Some drove mopeds in circles around the square, carrying out skids and angering bystanders.
"Thugs, thugs... The square is controlled by thugs," an old man chanted.
Some people still milling about in Tahrir said they were angered by the way the police handled the crowd overnight.
"I am here today because I heard about the violent treatment by the police of the protesters last night," Magdy Ebrahim, 28, an accountant, told Reuters.
He came too late.
Security officials, however, are said be on edge as tensions still simmer in Cairo heading into Friday and its weekly afternoon Muslim prayers -- the sparkpoint of so many protests throughout the region.