Violent clashes between  protesters staging a sit-in outside the Defence Ministry Headquarters in Cairo’s Abbasseya district and unknown assailants killed at least 20 people on Wednesday and left scores of others injured.

The violence began in the early hours of Wednesday when unidentified men in plain clothes attacked the peaceful sit-in  —apparently with the aim of dispersing the protesters who had camped out there for several days.

Supporters of Salafist former presidential candidate Hafez Abou Ismail had marched to Abbasseya on Friday evening to protest his exclusion from the presidential race. They were later joined by other activists: mainly liberals and members of the 6 April Movement. They all demanded an end to military rule and a swift  handover to a civilian government.

“What started as a peaceful  demonstration  has turned into a bloodbath,” cried Iman Mohamed, an activist who had joined the sit-in a couple of days earlier. She added that the assailants had fired gun shots and used Molotov cocktails and tear gas. Some of the protesters responded by hurling rocks and stones at the assailants, others engaged in fist fights.

“I saw several men wielding batons and another carrying a sword,” said Haytham Sallam, another protester who had arrived at the scene Wednesday morning.

“People dropped dead right in front of our eyes,”  he added.

There was a brief lull in the early morning hours before clashes erupted again at 9am and continued for several hours. Most of the dead had sustained fatal head injuries or had been shot in the head.  The attackers had also used bird shots and dozens of injured protesters were receiving treatment at a makeshift field  hospital set up at the scene or in the nearby Demerdash Hospital.

Some protesters suspected that the assailants were security  force members disguised  in plainclothes. “How else would you explain the use of tear gas and bird shots?” quizzed Sallam. Others said the use of “thugs” to break up protests had become “an all-too- familiar tactic “ adopted by some elements in  the government so that they would not directly take the blame for the violence themselves.

Military soldiers  and riot police set up barricades around the area but  most protesters said they had done little to break up the clashes or calm the situation. Seven political parties boycotted a meeting that had been called for Wednesday by the military council as rumours spread that the ruling SCAF was planning to postpone the presidential election scheduled for 23 and 24 May.

To allay concerns the Deputy Head of SCAF, General Sami Annan was quoted by Egyptian state television as saying the military was looking into transferring power to an elected president on 24 May (after the first round of elections) instead of at the end of June as had earlier been planned.

The announcement did little to quell public anger, as several protest marches to Abbasseya were organised later in the day by political parties and activists. Another million-person march has also been called for Friday by the Freedom and Justice Party to express outrage at the authorities’ response to the violence and pile pressure on SCAF to sack the government of Prime Minister Kamal el Ganzouri.

In another development, three presidential candidates have suspended their campaigns in honour of those who died in the latest wave of unrest.

Meanwhile back in Abbasseya, protesters issued fiery warnings to SCAF against any delay in the presidential election. ” If there’s any postponement, it will set off more unrest that would be difficult to contain,” warned activist Dina Nasr.

Journalist Shahira Amin resigned from her post as deputy head of state-run Nile TV in February 2011. Read why she resigned from the  “propaganda machine” here.