Egypt's Health Ministry says one person was killed and 71 injured after the army charged into a central Cairo square to disperse a protest.
Hundreds of soldiers stormed the square, beating protesters with sticks and firing volleys of gunfire in the early hours of the morning to disperse a demonstration carried over from the night before.
After the soldiers withdrew, protesters reoccupied the square, armed themselves with makeshift weapons and sealed off the entrances with barbed wire left by the military.
An army spokesman said the forces fired blanks and not live rounds to warn protesters.
The troops eventually withdrew, however, enabling demonstrators to reoccupy the square and block the streets leading into it. Armed with sticks and other makeshift weapons, they vowed not to leave until the defense minister, the titular head of state, has resigned.
A force of around 300 soldiers swept into the square around 3 a.m. and waded into a tent camp in the center where protesters had formed a human cordon to protect several army officers who had joined their demonstration in defiance of their superiors.
The troops dragged an unknown number of protesters away, throwing them into police trucks, eyewitnesses said.
"I saw women being slapped in the face, women being kicked," cried one female protester, who took refuge in a nearby mosque. Troops surrounded the mosque and heavy gunfire was heard for hours. Protesters in the mosque reported large numbers of injured, including several wounded by gunfire.
The nearby Mounira hospital said it treated 15 wounded demonstrators.
The military issued a statement afterward blaming "outlaws" for rioting and violating the country's 2 a.m. to 5 a.m. curfew, and asserted that no one was harmed or arrested.
"The armed forces stress that they will not tolerate any acts of rioting or any act that harms the interest of the country and the people," it said.
Black smoke rose in the sky as the sun came up in Cairo, after three vehicles, including two troops carriers, were set on fire.
The square was filled with shattered glass, stones and debris from the fighting, in a scene reminiscent of the protests in January that brought down the regime of Hosni Mubarak. The glass storefront of a KFC on the square was also smashed.
"We are staging a sit-in until the field marshal is prosecuted," said Anas Esmat, a 22-year-old university student in the square as protesters dragged debris and barbed wire to seal off the streets leading into the square.
"The people want the fall of the field marshal," chanted protesters, in a variation on the chant that has become famous across the Middle East with protests calling for regime change. "Tantawi is Mubarak and Mubarak is Tantawi," went another chant, explicitly equating Field Marshal Mohammed Hussein Tantawi, the defense minister, with the president who once appointed him.
The clashes came hours after hundreds of thousands massed in Tahrir Square on Friday in one of the biggest protests in weeks, demanding that the military prosecute ousted president Hosni Mubarak and his family for alleged corruption.
The rally was a show of the increasing impatience and mistrust that many Egyptians feel toward the military, which took over when Mubarak was forced out of office on Feb. 11. Some protesters accuse the military leadership of protecting Mubarak — a former military man himself — and more broadly, many are unclear on the army's intentions in the country's transition.
More than in previous protests, chants and banners Friday directly criticized the military's Supreme Council of the Armed Forces and Tantawi, a former Mubarak loyalist.
A number of army officers in uniform joined the protesters, some of them accusing the Supreme Council of corruption in speeches to the crowd. After dark, hundreds of protesters remained in the square, intending to camp out with the officers.
Before the pre-dawn assault, military police tried several times to move in and detain the officers but were pushed back by protesters. At one point, protesters pushed and shoved an army general, tearing his cap from his head.
After the attack in the early hours of the morning, the scene was chaotic. Inside the mosque, families who had camped out in the protest tent searched for children who got lost in the mayhem. Outside, protesters scuffled with soldiers on side streets, chanting, "Marshal, tell your soldiers, we aren't leaving."
Near the famed Egyptian Museum, which overlooks the square, protesters trying to flee were blocked by soldiers, who hit them and knocked them to the ground before dragging them away.
"I saw them detain a bunch at the museum. They were beating some pretty badly," said one protester, Loai Nagati.
The confrontation was a sharp contrast to the warmth protesters expressed toward the military during the 18-day wave of mass demonstrations that led to Mubarak's ouster and in the days immediately following. Many praised the military for refusing to fire on protesters, and welcomed the army for stepping in to rule.
But tensions have since grown. Reports have emerged of some protesters arrested and tortured by the military in past weeks. Anger has also grown over the failure so far to prosecute Mubarak and his family.
Corruption was widespread under Mubarak's 29-year-rule, and resentment particularly accelerated in the last years of his rule, as his son Gamal — an investment banker-turned-politician — rose to prominence and brought into power a group of millionaire tycoons who implemented a program of economic liberalization. Several of those businessmen-politicians are now under investigation for allegedly using their positions to amass personal fortunes.
Trying to assuage the public anger, the military appeared to be trying to accelerate prosecutions and has denied it is protecting the ousted president.
But so far, there has been no move against Mubarak or Gamal, who was widely seen as his choice as successor. Since his ouster, Mubarak and his family have been under house arrest at a presidential palace in the Red Sea resort of Sharm el-Sheikh, their assets frozen.
In a further challenge to the military, more than 1,000 protesters on Friday evening marched on the Israeli Embassy in Cairo, denouncing Israeli airstrikes against the Gaza Strip earlier in the day.
The demonstrators, including a large contingent of Muslim Brotherhood members, were stopped by a military checkpoint yards (meters) away from the residential building where the embassy is located, overlooking the Nile River. They chanted demands that the embassy be shut down and that Egypt stop selling natural gas to Israel.
The march has promised Egyptians greater freedom of expression but at the same time have sought to reassure Israel and its ally the United States that the fall of Mubarak would not mean an anti-Israeli turn in Egypt's foreign policy.
The Associated Press contributed to this report.