At least 11 people were killed in clashes that broke out early Wednesday during a demonstration outside the Egyptian Defense Ministry, officials said, marring the official start this week of campaigning for the country’s upcoming presidential election.

Some prominent candidates temporarily suspended campaign activities and criticized Egypt’s ruling military chiefs for failing to stop the bloodshed while seeking to capitalize on the events. As the death toll rose, the violence quickly became a rallying point for a cross-section of liberal, youth and Islamist groups angered by what they describe as a botched transition under military rule.

Egyptian security forces refrained from intervening during the hours when the violence in Cairo’s Abbasiya district was at its height, witnesses said, leading many to question whether they were unwilling or unable to stop it.

The demonstration began as a sit-in last Friday to protest the disqualification of Hazem Abu Ismail, a prominent Islamic candidate, from the election scheduled for May 23. But it swelled as other Egyptians joined in with a long list of grievances against the military rulers, including the barring of other candidates, including two other front-runners.

Men armed with guns and handmade explosives attacked dozens of protesters early Wednesday, and protesters retaliated by throwing rocks and wielding rods, according to witnesses.

The April 6 youth movement, one of the main instigators of last year’s popular revolt, said one of its members was among those killed Wednesday.

“If this blood was spilled and people were martyred and dozens injured only because they demanded” a fair election, the group said in a statement, “then what is the military going to do to us in case we see and reveal fraud?”

Anti-military protesters contend that plainclothes assailants who strike at these types of demonstrations are acting at the behest of the armed forces. Mohamed Morsi, the presidential candidate of the Muslim Brotherhood’s Freedom and Justice Party, who was among those who temporarily suspended campaigning, said Wednesday that the ruling generals Wednesday bore ultimate responsibility for the carnage.

“The killing is systematic and not random,” Morsi told reporters. “Even if they don’t have a hand in these clashes, they are still responsible.”

Abdel-Moneim Aboul Fotoh, the other prominent Islamic candidate remaining in the race, joined a throng of demonstrators who marched from downtown Cairo to Abbasiya on Wednesday night.

The clashes had tapered off about noon as the military and police deployed security forces in riot gear to the site. But demonstrators said they planned to camp out outside the ministry overnight.

“Down with military rule!” they chanted.