Pre-election violence has erupted in the Egyptian capital, Cairo, killing at least 11 people, wounding more than 100 others, and prompting several presidential candidates to suspend their campaigns.

Egyptian medical and security sources confirmed the death toll in Wednesday's fighting, which began at dawn when assailants raided a protest camp occupied by hundreds of activists opposed to the military-backed government.

The mostly Islamist protesters had been camping near the Egyptian defense ministry in Cairo's Abbassiya district since Saturday, demanding an immediate end to military rule in Egypt. The protesters fought back against the assailants, described by some witnesses as pro-government “thugs.” The rival groups attacked each other with firebombs and stones. Gunfire also was heard at the scene.

Egypt's military rulers initially did not intervene in the fighting. They sent in troops and armored vehicles to separate the two sides after several hours.

The two leading Islamist candidates for the Egyptian presidency responded to the violence by suspending their campaigns for the election, which begins on May 23 and 24.

Mohamed Mursi of the Muslim Brotherhood announced a two-day suspension in solidarity with the victims. The Brotherhood also declared a boycott of a meeting with Egypt's ruling military council planned for later on Wednesday.

The other leading Islamist candidate, Abdel Moneim Abol Fotouh, cancelled his next campaign events in protest at how authorities handled the Cairo street battles.

Egypt's presidential election will be the first since a popular uprising ousted longtime autocratic leader Hosni Mubarak in February 2011.

The military council that took over from Mr. Mubarak has promised a democratic transition and a transfer of power to an elected president by July 1st. But, Egypt's generals have faced strong domestic criticism for their handling of that process, which has been plagued by periodic eruptions of deadly violence, often surrounding anti-government protests in major cities.

Many of the protesters camped outside the Egyptian defense ministry are Islamists who were angered by the ruling military's decision to bar ultraconservative Islamist cleric Hazem Abu Ismail from standing in the presidential contest. Egypt's election commission disqualified Abu Ismail because his mother had taken joint U.S. citizenship.

Some liberal pro-democracy activists had joined the Islamists at the encampment in calling for Egypt's ruling generals to step down immediately.