Updated at 1:27 p.m. ET
CAIRO - Security forces fired tear gas and clashed Monday with several thousand protesters in Cairo's Tahrir Square in the third straight day of violence that has killed at least 24 people and has turned into the most sustained challenge yet to the rule of Egypt's military.
After months of growing tensions between the two sides, revolutionary activists threw down the gauntlet, vowing they would not leave the iconic downtown roundabout until the ruling generals leave power or at least set a clear date for doing so.
As the death toll mounted Monday, a nurse at the Egyptian Health Ministry told CBS News correspondent Elizabeth Palmer that some of those killed in the melee died from gunshot wounds inflicted by live ammunition. While it was unclear who shot the bullets -- the government has said only that rubber bullets are being used -- Palmer said she saw nobody armed in Tahrir Square on Monday apart from the security forces.
Palmer reports that hundreds more protesters were flooding into the square on Monday afternoon, including a large group which marched from Cairo University led by hunger striker Leila Souif, whose son Alla Abdel Fattah has been in prison for 3 weeks, accused of attacking a soldier and "insulting the Supreme Military Council."
One Egyptian human rights worker, who was behind the police front lines in the clashes over the weekend as an observer, tells CBS News she heard a senior officer ordering his men to take aim at the protesters' heads with rubber bullets. Numerous videos posted to the Internet allegedly show brutality by Egyptian police, with some officers beating protesters even as they lie apparently unconscious.
The videos could not be immediately confirmed, but the Health Ministry nurse who spoke to Palmer said some of those killed had died of head injuries and internal bleeding after severe beatings.
"We're not going anywhere," protester Mohammed Radwan said after security forces tried unsuccessfully to push the crowds out of Tahrir on Sunday.
Repeated attempts by security forces and military police over the weekend have failed to eject them from the square, and the rising death toll has only brought out more and angrier protesters.
But the bid to launch what some tout as a "second revolution" is snarled by politics, with Egypt coming up on key parliament elections only a week away. The loose coalition of groups that led the 18-day uprising that ousted Hosni Mubarak in February is fragmented. In particular, the Muslim Brotherhood, which gave the first revolution powerful muscle, so far refuses to take to the streets again, fearing the turmoil will derail elections it expects to dominate.
And those in the square have yet to find cohesion on a picture for what's next. Some want the military out immediately. Others would be happy with a set date in the near future for them to quit power. Many want the military to transfer power to a national unity government.
"We want the council to leave immediately so we can continue our revolution, which the military sold out," said Mohammed Ali, a shoemaker among the protesters, referring to the Supreme Council of the Armed Forces. "A civilian Cabinet from the square is what we want."
Throughout the day, young activists skirmished with black-clad police, hurling stones and firebombs and throwing back the tear gas canisters being fired by police into the square, which was the epicenter of the anti-Mubarak protest movement. Sounds of gunfire crackled around the square, and a constant stream of injured protesters bloodied from rubber bullets or overcome by gas were brought into makeshift clinics set out on sidewalks, where volunteer doctors scrambled from patient to patient.
An Egyptian morgue official said the toll had climbed to 24 dead since the violence began Saturday a jump from the toll of five dead around nightfall Sunday, reflecting the ferocity of fighting through the night. The official spoke on condition of because he was not authorized to release the numbers. Hundreds have been injured, according to doctors in the square.
The eruption of violence, which began Saturday, reflects the frustration and confusion that has mired Egypt's revolution since Mubarak fell and the military stepped in to take power. Protesters also marched Monday other cities, including thousands of students in the coastal city of Alexandria.
Activists and many in the public accuse the ruling Supreme Council of the Armed Forces of seeking to hold on to power, and they fear that no matter who wins the election the military will dominate the next government just as they have the current, interim one they appointed months ago. Many Egyptians are also frustrated by the failure of the military or the caretaker government to conduct any real reforms, quiet widespread insecurity or salvage a rapidly worsening economy.