Al Jazeera's Cairo bureau chief Ayman Mohyeldin said Monday that he was blindfolded, handcuffed and taken into custody by Egyptian military police the previous day.
He was released after nine hours in detention.
Mohyeldin told the network Monday that he and other detainees were treated like "prisoners of war."
"As I was making my way into Liberation Square, I was essentially stopped by the Egyptian military, and there was a young recruit there who asked me for my identification," he explained. "When I presented him with my identification, he asked me 'What you are coming to do?'"
"I simply said I was a journalist, I didn't really have any major equipment on me, just a small camera and my cellphones. Immediately it seemed like he was taken aback, surprised perhaps by my identity. At that time they didn't know who I was working for, and they didn't ask me, really. It was just the mere fact that I was a journalist who was trying to go into Liberation Square that seemed to be enough for them to take me for further questioning."
Mohyeldin, a US citizen, was then taken to a nearby makeshift holding area.
"I was handcuffed with plastic wire. I was blindfolded, and I was made to sit on the pavement for about five hours or so with several other people including journalists who were there."
He was eventually interrogated and asked "intimidating" questions about what he thought of the protests.
"They were ultimately saying to me: What I was doing in Egypt? Why don't I just go back the the United States where I came from and why I was trying to project a negative image of Egypt to the outside world?"
Mohyeldin described being held with several other journalists and protesters captured in Liberation Square.
"I can tell you from what I saw and from what I heard, a lot of these people were beaten up. They were very -- the military was dealing with them in a very aggressive manner. They were slapped, they were kicked," he said.
"I don't think it was a matter of trying to coerce them for information, but in essence, the military was dealing with these people as prisoners of war," Mohyeldin continued.
"These were individuals who were trying to plead for their safety, for their innocence. Many of them were crying, saying they were simply just caught up in the wrong moment. But the military showed no mercy, and on a few occasions they really roughed them up pretty badly. They kicked them in the back of their heads."
"One of the soldiers that was there had with him a small Taser gun. He was instantly instigating that Taser to try to scare the prisoners, or the detainees, really, into submission and behaving. Many of them had their shirts taken off of them. And many of them were also severely whipped and slapped and essentially pushed around in a way to kind of control them even though they weren't doing anything that was very disobedient," he added.
Thousands of Egyptians returned to Liberation Square Tuesday in opposition to President Hosni Mubarak's regime. Many said that Tuesday's demonstrations were the biggest so far.