Twenty were killed and scores were wounded in Cairo clashes that erupted on Wednesday outside the Egyptian Defense Ministry after a group of "unidentified assailants" attacked demonstrators protesting continued military rule.
A military junta took interim control of Egypt following a popular uprising that led to the ouster of long-time president Hosni Mubarak on 11 February 2011.
The generals have promised to transfer power to a civilian administration by January 1, but daily rallies demanding the junta step-down immediately continue to be staged.
Security officials in Cairo who spoke on condition of anonymity told reporters that the clashes broke out at dawn when a group of "unidentified assailants" set upon several hundred protesters who had been camped out in the area since early Saturday, when 119 were injured in a violent flare-up.
Wednesday's violence led several presidential contenders to shift the focus of their campaigns to the perceived failure of the interim junta to stop the bloodshed.
Some politicians from the newly elected Islamist-dominated parliament cancelled meetings with various generals as a show of disproval.
Initial reports on the ground indicated the assailants were soldiers in plainclothes who started the clashes by hurling cinder blocks at the demonstrators, but it remains unclear if that was actually the case.
Nor is it clear the victims were all protesters, or if any of the attackers were among the dead.
Egypt’s pro-military state media said the assailants were residents angered by the disruption caused by the protests to life in their neighborhood.
However, some pro-democracy activists claim the assailants operate with the blessing of the police or the military, or may be on their payroll.
The clashes resumed a few hours later in late morning, but came to an end when lines of riot police and troops backed by armored vehicles moved in to separate the two sides.
Large numbers of black-clad military police in riot gear have been deployed to the area.
Video footage broadcast on Egyptian television showed pitched battles between the two sides on residential streets close to the Defense Ministry in the Cairo district of Abbasiyah.
Officials reported that rocks, clubs, firearms, and firebombs were used in the clashes.
Most of the protesters were supporters of Hazem Salah Abu Ismail, an ultraconservative Islamist who was thrown out of the presidential race because his mother holds dual Egyptian-US citizenship, which violates eligibility rules to run in the election.
There have been unconfirmed media reports that some of the Abu Ismail supporters brought firearms to their encampment after an attack by assailants earlier this week that left one protester dead.