BBC News is reporting that at least 20 are dead in Cairo as a result of an attack on an anti-military protest near the Ministry of Defense.
The attackers used rocks, clubs, fireboombs, and shotguns, BBC News reports.
According to AFP, the protesters had been camping out to protest against military rule.
A military source says the army deployed troops in Cairo to stop the clashes, but BBC News reports that the violence went on for 6 hours before anything was done.
AFP reports that four presidential candidates have announced they are suspending their campaigns because of the killings and the way in which they were dealt with by authorities.
According to BBC News, many of the protesters were supporters of a Salafist preacher who was not permitted to run in the Egyptian presidential election.
Hazem Abu Ismali was disqualified from the race when it was discovered that his mother had Egyptian and US nationality, which violated rules made in a constitutional declaration set forth after Hosni Mubarak was forced to step down.
Abu Ismali was convinced this was all part of a plot by military authorities, but no proof of that was ever found, BBC News reports.
AFP reports that the Muslim Brotherhood's Mohammad Mursi has decided to stop campaigning for 2 days in "solidarity with the protesters."
His main Islamist rival has canceled Abdel Moneim Abul Fotouh canceled all activity for the day, and leftist candidates, Khaled Ali and Hamdeen Sabbahi have also announced plans to suspend their campaigns.
Ahmed Raafat who was at the demonstration with friends told BBC News, , the attacks were like a "massacre."
"I saw several people with head injuries and two people died in front of me. There was a lot of blood everywhere."
The Montreal Gazette reports that other witnesses said they heard shooting and that the protesters responded to the "thugs" just as violently.
The health ministry said more than 150 people were injured in the attacks and that many were receiving treatment at a nearby field clinic.
Amr Mussa, the front runner in the race said the violence was "proof of the need to put an end to the transitional period according to the timetable, without delay, AFP reports.
The military originally intended to transfer power by June, but BBC News reports that General Sami Annan was looking into the possibility of transferring power by as soon as May 24.