Clashes have erupted between assailants and supporters of Egypt's Islamist political parties who had gathered near the defence ministry in Cairo, leaving 11 people dead and nearly 50 wounded, security and hospital officials said.
The violence on Wednesday is the latest episode in more than a year of turmoil in Egypt following the toppling of longtime ruler Hosni Mubarak and will likely fuel more tensions just three weeks ahead of presidential elections.
The military generals who took over from Mubarak in February last year have promised to hand over power to a civilian administration by July 1, but that has not stopped rallies demanding the generals leave immediately.
The security officials said the clashes broke out at dawn when the assailants set upon several hundred protesters who had camped out in the area since early Saturday to press their demand for the military to go.
Hospital officials said nine of the 11 died of gunshot wounds to the head while two people were stabbed to death. The health ministry only confirmed nine were killed and 49 were injured.
In response to the clashes, military and riot vehicles were deployed to the area later on Wednesday to quell the violence.
"Eight armoured personnel carriers from the military central zone entered the Abassiya area to disperse the fighting between protesters, and not to disperse the peaceful demonstrators," an army statement said.
"However, protesters attacked the armed forces. The armed forces have orders to hold their ground."
The state news agency MENA said "thugs", some of them with guns, had assaulted the protesters.
The violence casts a shadow over the presidential election due to begin on May 23 and 24, with a runoff in June, and
highlights the fragility of Egypt's transition to democracy which has been punctuated by violence and political bickering.
"This has been an ongoing sit-in for the past five days," Al Jazeera's Rawya Rageh reported from central Cairo, saying that the latest skirmishes began early on Wednesday morning in the neighbourhood near the Abbasiya subway station.
There had been some scuffles near the defence ministry in recent days, but protests had been broadly peaceful.
Residents gathered around a police station in the vicinity after the clashes on Wednesday, demanding that police disperse the protesters.
Some of the protesters are supporters of an ultraconservative Islamist presidential hopeful, Hazem Abu Ismail, who was barred from the upcoming presidential election because his mother held dual Egyptian-US citizenship, in violation of eligibility rules.
"[The sit-in] initially started off as one that was called for by the angry supporters of Abu Ismail, who was disqualified from the race; people gathered there to protest his disqualification," our correspondent said.
"But as with most protests over the past few months, it escalated into something bigger into a protest against the overall military practices and the way the ruling military council has been running the country over the past 14 months."
Rageh said that among those killed on Wednesday were members of the April 6 movement as well as independent protesters.
"[Protesters] have been coming under repeated attacks and skirmishes from people in the neighbourhood; people in plain clothes who have been unhappy about their presence in the predominantly residential neighbourhood," she said.
The April 6 Youth Movement decried the "massacres" and demanded the army be held to account for its "crimes committed against the revolution and revolutionaries".
"These practices are a continuation of the cleansing and killing methods which the army council uses to suppress the
revolution," April 6 said in a statement.
Meanwhile, two presidential candidates decided to temporarily suspend their campaigns over the clashes.
The Muslim Brotherhood candidate Mohammed Mursi told reporters he decided to suspend his campaign for 48 hours "in solidarity with the protesters", while his main Islamist rival, Abdel Moneim Abul Fotouh, cancelled all his events for the day over the clashes, a campaign official told AFP.
Our correspondent adds: "We have seen several candidates suspend their campaigning. Whether this will lead to a wider suspension from more candidates who are campaigning remains to be seen."