CAIRO — For the third time in a week, deadly clashes erupted near Egypt’s Defense Ministry when military policemen fired tear gas and water cannons and threw rocks to disperse tens of thousands of protesters, in a sign of growing tensions as the country nears the end of a turbulent 15-month political transition.

The latest bloodshed, which left at least two people dead and hundreds injured, started after thousands of protesters marched peacefully to the ministry, defying a warning by the ruling military council not to approach the building. The fighting started quickly, seesawed near a front line for hours, and then spread, in skirmishes that left bloodstains on the sidewalks of the surrounding neighborhood.

About 5 p.m., backed by reinforcements in armored vehicles — and armed residents — the army had scattered the throngs of protesters and set up barbed wire checkpoints as the military announced a curfew from 11 p.m. to 7 a.m.

The clashes came a day after the generals who took power after President Hosni Mubarak’s ouster delivered an impassioned defense of their rule, asserting their authority during the transition in a televised news conference, as well as their determination to hand over power after the presidential election that begins later this month.

The violence this week reflected protesters’ doubts about the military’s intentions and anger at the generals over bloody episodes that have occurred during the transition. And it laid bare a current of anxiety that is tempering excitement about the elections, as interest groups fight for influence and resentments come to the fore.

The groups include ultraconservative Islamists who support Hazem Salah Abu Ismail, a presidential candidate who was disqualified after it was revealed that his mother held an American passport before her death. Mr. Abu Ismail’s supporters have camped outside the ministry for days, protesting the disqualification. On Friday, they were joined by a broad range of political groups, mobilized by violence earlier in the week near the Defense Ministry that left at least 11 people dead.

At a news conference on Thursday, a spokesman for the military pointedly warned protesters against approaching the ministry headquarters.

“The right to self-defense and the honor of the military compel the armed forces to protect and defend the Ministry of Defense and all military establishments,” the spokesman, Gen. Mokhtar el-Mola, said.

But tens of thousands of demonstrators insisted on defying the general. When they reached the neighborhood of Abbaseya, where the ministry is, they found hundreds of military police waiting. The clashes started quickly, with rock throwing by both sides as the protesters were doused by water cannons.

By about 4 p.m., the area was bathed in tear gas and an army helicopter circled overhead. Within an hour, the army was pressing forward, amid sounds of gunfire that may have been birdshot — a favorite ammunition used by the security services. A fire spread in the protesters’ encampment, and people retreated into the neighborhood where riot policemen were waiting along with people who appeared to be residents, armed with sticks. Some stood outside their buildings in flip-flops, handguns tucked into their pants.

One man told his friends that the Islamists were in the neighborhood to attack a nearby cathedral. “They call us thugs,” the man said, referring to the conviction among many protesters that they are being attacked by plainclothes enforcers hired by the security services.

The man and his friends were one of several groups that roamed the streets as the army took control. Several groups accosted bearded men and beat them before handing them over to the military police. At the entrance to a hospital, people gathered around an arriving ambulance carrying a man with deep cuts to his head. As paramedics tried to wheel his gurney inside, two men grabbed it and tried to take the injured man down the street. “We don’t want him here,” one of the men screamed. “No Salafis! No Brotherhood!” a woman yelled, referring to ultraconservative Islamists and the Muslim Brotherhood. An officer scuffled with the residents, and scolded a medical worker who tried to complain.

“You’re a hospital,” the officer said. “Take him inside.”

The military council has already vowed not to let the protests postpone the presidential election, set to begin May 23. But several leading presidential candidates have suspended their campaigns, after deaths earlier this week.

As a matter of politics, much will depend on where the blame settles. It was unclear whether the chaos might benefit the candidates running on strong law and order platforms — like Amr Moussa, a former foreign minister under Mr. Mubarak — or those focused on wresting power from the hands of the military.

In Abbaseya, people in the streets on Friday made their preferences clear. About 6 p.m., as armored vehicles flooded the neighborhood, many people clapped and cheered. Young men on scooters provided escorts, with one holding a large portrait of Field Marshal Mohamed Hussein Tantawi, who leads the ruling military council. The soldiers, elated, waved and fired their guns into the air. David D. Kirkpatrick contributed reporting. (Copyright 2012 The New York Times Company 05/05/12)