© Amr Nabil/APMuslim Brotherhood supporters at a rally in Cairo. Wednesday's violence comes three weeks ahead of presidential elections in Egypt.
At least nine protesters have been killed and 45 injured in a dawn attack on protesters gathered outside Egypt's ministry of defence, according to the health officials.

Clashes continued on Wednesday morning between protesters and the unidentified assailants, who threw petrol bombs and fired live ammunition, birdshot and teargas, according to witnesses.

"There is a deluge of blood on the street which extends for many metres. One injured man had his back sliced by the thugs," said Abdelrahman Hany, a rights advocate at the Arabic Network for Human Rights Information organisation who was present when the latest round of attacks began.

Hany said he believed the attackers were linked to the state security apparatus. "How else would they possess teargas to fire at us?" he asked.

Protesters had camped in Tahrir Square for a week before deciding on an impromptu march to the ministry of defence in east Cairo last Friday, where the sit-in resumed.

The sit-in was first attacked on Saturday night, when at least one person was reported killed. That attack comprised nail bombs, birdshots and automatic gunfire and lasted until early on Sunday morning, with no intervention by the military troops present.

Many of the protesters are supporters of Hazem Abu Ismail, an ultraconservative Islamist who was thrown out of the presidential race because his mother held dual Egyptian-US citizenship, which violates electoral rules.

But the sit-in also included members of secular movements such as the unaffiliated Revolutionaries Without Direction, an umbrella group hoping to gather disparate forces with the aim of removing the military junta that has ruled Egypt during the transitional period.

A member of that group, Mohamed Dahaby, accused the interior ministry of hiring the attackers at the behest of the military and said the group was planning a major demonstration near the ministry on Friday. "Next Friday is the end for military rule," he said.

Liberal pro-democracy groups, which were also involved in the protests demanding the army return immediately to the barracks, condemned the attack at the defence ministry.

The 6 April youth movement decried the "massacres" and demanded that 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," the group said in a statement.