By 7am (local time) on Saturday morning, army and central security troops appeared to have withdrawn, leaving the square to protesters who set vehicles on fire and began setting up barricades made of furniture and left-behind barbed wire.
Hundreds of army and security forces troops had stormed the square earlier, in an attempt to disperse the thousands of protesters.
In scenes reminiscent of the violent 18-day uprising that ousted longtime President Mubarak in February, protesters and riot police threw rocks at each other, and security forces responded by firing tear gas, witnesses said.
Groups of protesters rallying around the southeast corner of the square threw bottles and possibly petrol firebombs at riot police, Michelle May, a freelance journalist, told Al Jazeera.
One of the main roads running east from Tahrir Square towards Talaat Harb Square was virtually empty, and gunfire seemed to have subsided, a witness said.
Tens of thousands of protesters had flooded into the square on Friday in one of the largest demonstrations since Mubarak stepped down on February 11.
The protesters called for the Supreme Council of the Armed Forces, which nows runs the country, to honour their demands, which include prosecuting a number of former high-ranking regime officials and Mubarak himself.
The protesters had been joined by perhaps as many as 20 military officers, who had been under orders not to participate. Demonstrators stayed in the square past the military curfew, which which runs from 2am to 5am, saying they wanted to protect the officers who joined.
When security forces stormed the square, some of the protesting army officers managed to escape, while others were arrested, witnesses said.
Loai Nagati, a student, told Al Jazeera that military police and central security forces took some protesters and beat them, but that nobody had been shot. Speaking while gunfire echoed in the background, he said that some of the army officers who joined the protests had been arrested by security forces.
Amr Bassiouny, who was standing at the square's south entrance near the old campus of the American University in Cairo, told Al Jazeera that hundreds of soldiers backed by eight armoured vehicles entered the square from that direction at around 3am.
The soldiers formed a semi-circle around the south end of the square and advanced towards a tent in the middle where the protesting army officers had been kept. Soldiers could be seen tearing down the tent in an amateur video posted on YouTube.
For 10 or 15 minutes, the protesters and soldiers faced each other, said Sanaa Seif, who had been in the square since 11pm. Protesters chanted "Peaceful, peaceful," and "The people and the army, hand in hand", but the soldiers moved forward again, firing "non-stop" into the air, she said.
Guns fired, rocks thrown
Most of the protesters retreated after the army entered the square, witnesses said. Bassiouny ran to the west side of the square, which leads to Kasr el-Nil Bridge, and found more troops entering from that direction.
Protesters and army soldiers threw rocks at each other, and at least four injured protesters had to be carried away, he said. Soldiers fired their guns into metal shopfronts, sending sparks flying and bullets ricocheting, apparently to scare away the protesters, Storey said.
At one point, he said, security forces clad in riot gear chanted, cheered and shook each others' hands after driving the protesters away.
Other central security and army forces had been stationed to the north of Tahrir Square next to the Egyptian Museum, which military police have turned into a makeshift detention centre.
Arbitrary arrest allegations
In recent weeks, activists have accused the army of making arbitrary arrests, abusing and torturing prisoners, and subjecting detainees to rapid military justice - all complaints that had fuelled mass anger against Mubarak's government.
The increasingly icy relationship between the ruling military council and the youth-driven protest movement was one reason many had returned to the square on Friday. But as the protest thinned and only a few people remained, demonstrators vowed to protect the army officers who had joined them, using loudspeakers to urge others to defend the soldiers with their lives, Seif said.
Though some of the protesting army officers were reportedly arrested, seven or eight escaped the square, Bassiouny said.
Seif said she saw a group of people leading some of the protesting officers out of the square.
She said she hoped the crackdown would bring more people out into the street to protest.
"I hope so, I mean it happened before, but I think it's getting better, because people are now more aware that the army is not really that loyal to the revolution," she said.
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