Protesters threw rocks at troops guarding Egypt's Defense Ministry on Friday as thousands marched in Cairo to denounce violence against demonstrators and the exclusion of candidates from the presidential election.The crowd hurled projectiles and insults at the soldiers sent to defend the ministry after 11 people were killed in clashes there on Wednesday, and called for the overthrow of the head of the ruling army council, Field Marshal Hussein Tantawi.The army fired back water cannon then teargas and riot police surged towards the crowd with batons. Scores of wounded protesters were taken away on motorcycles and dozens of soldiers were injured."O Tantawi, good morning, this is your last day," shouted the crowd, and "Field Marshal leave, the people are dangerous".The street violence comes less than three weeks before an election that represents the first chance for Egyptians to freely choose their leader. A successful vote would mark the most important step in a messy transition to democracy since the overthrow of autocratic leader Hosni Mubarak 15 months ago.Last-minute changes to the line-up of contenders, bickering over a new constitution and suspicion that the military will continue wielding power after a new president is chosen are making for a chaotic backdrop to the campaign.The troops pressed forward when protesters began cutting through barbed wire used to seal off the ministry building in Cairo's central Abbasiya district.Protesters ripped down a metal fence at an underground railway construction site to build a barricade. Some cried "God is Greatest" as army helicopters swooped overhead.The teargas scattered the crowd hundreds of meters down the rock-strewn streets where they regrouped. Troops blocked off a street to the ministry using armored personnel carriers and some fired shots in the air."The crowd is coming here with sharp weapons. We have batons and water cannon and teargas to disperse them," said one commander. "Some of them believe if they kill a soldier they will go to heaven. What do you expect us to do?"The Health Ministry said 59 people were injured, most of them from inhaling teargas, and five were taken to hospital.As dusk approached, gunfire could be heard close to a mosque in the center of the capital.