(CNN) -- In the middle of a loud, violent brawl in Tehran, Iran, anti-government protesters manage to corner a handful of riot police who were sent to combat them.
As the crowd pushes the police against a wall -- with screams coming from all directions -- a protester points his finger at them. "Why are you doing this?" he yells.
One of the police -- the only one whose helmet is off, his face apparently bloody -- responds. "I'm sorry," he says. "I'm sorry." The other police stand still, trapped by the crowd's grasp.
Then the protester says something else, in one of the most telling signs of the historic anti-government rebellion sweeping through the streets of Iran.
He demands that the police call Ayatollah Khamenei -- the supreme leader of the nation's hardline Islamic government -- a "bastard."
Reports including photos from the scene indicate the incident took place Sunday.
The video, leaked to the world via YouTube despite a widespread crackdown by Iran's government, is a sign of what is under way in the country: an unprecedented groundswell that shows no sign of abating, six months after a disputed presidential election started it all.
In the latest series of clashes that sparked over the weekend, eight people were killed, according to Iran's Supreme National Security Council -- making it the deadliest incidents since June.
The fighting came on the anniversary of Ashura, a major Shiite Muslim Holy day that provided a critical religious backdrop. Ashura marks the death of Imam Hussein, grandson of Prophet Mohammed, as a martyr. Large crowds pour into streets each year for the observance.
Some demonstrators over the weekend compared Khamenei to Yazid, the caliph who killed Imam Hussein.
As the country's religious leaders called for arrests of protesters, the demonstrators asked how the government would dare to round up people who had gathered for events marking the religious occasion.
Still, hundreds were arrested. One of the country's national security officials called openly for demonstrators to be rounded up and carted off.
Videos posted online from Tehran show protesters with their heads covered in blood, in some cases requiring help walking from fellow demonstrators. Witnesses said members of the Basij, the government's militia, were smashing protesters on the head with their batons.
Two other gruesome videos show protesters in the streets who appear to have just been killed.
The videos also seem to show a growing fearlessness, a fierceness among the demonstrators that has people around the world asking whether the revolt will one day spell the end of Iran's Islamic republic.
CNN's Reza Sayah, an Iran native who covers the region, called it an unprecedented uprising, presenting "the most significant challenge" the Islamic republic has faced since its government came to power through a revolution 30 years ago.
"Its strength, its power over these past 30 years has been repression, has been intimidation of anyone who's dissented," but the government hasn't managed to quell this rebellion, Sayah said. "And you look at this opposition movement, and you have to ask yourself how. They don't have a strong leader. They don't have a structure. They don't have an organization. But somehow they manage to mobilize and move out."
Trita Parsi, president of the National Iranian American Council in Washington, D.C. -- a public critic of Iran's hardline government -- told CNN's "American Morning, "I think this may actually turn out to be a breaking point. What we've seen here is how the opposition, six months after the fraud in elections, still have a lot of fight in them. I think they've taken the Iranian authorities by surprise. They're still coming out in huge numbers, and morale seems to be stronger amongst the opposition than among the security forces at this point.
"This could very well end up being one of those indicators that this is not just going to end -- this is going to go for something that can be causing a dramatic change, not only in Iran but in the region as a whole."
The Iranian government presents a very different story. Through state-run media, the government has insisted that security forces have not killed anyone.
The state has also said it believes some of the videos may have been staged in order to make the government look bad.
The English Web site of state-run news agency IRNA led Monday with a story about Iran's president, Mahmoud Ahmadinejad, planning a visit to Tajikistan. Of about 20 headlines on the main screen of the Web site, none mentioned the protests.
Iran's media blackout made it difficult to verify accounts that leaked out.
Among the stories getting a great deal of attention around the world Monday was a suggestion that the body of Iran's opposition leader's nephew, who was among those killed over the weekend, had disappeared.
The reformist Web site Parlemannews reported Sunday that Saeed Ali Mousavi, nephew of opposition leader Mir Hossein Mousavi, was among the dead.
Iran's state-run Press TV quoted unnamed police officials as identifying one of the dead as "Seyyed Ali Mousavi."
On Monday, Parlemannews said the body had disappeared.
While such details could not be confirmed by CNN, it was clear that government actions in general against the protesters were fueling the protests -- not just among young Iranians seeking change, but among some older Iranians who once supported the Islamic regime.
On Saturday evening, a pro-government mob barged into a mosque where former president and reformist leader Mohammad Khatami was speaking. Khatami's supporters fought back, and word spread throughout the country.
Khatami is a respected cleric, a former elected leader.
The protests also came as Iranians were mourning the Grand Ayatollah Hussein Ali Montazeri, a key figure in the 1979 Iranian revolution. Montazeri went on to become one of the government's most vocal critics.
Robin Wright, author of the book "Dreams and Shadows: The Future of the Middle East," told CNN on Monday that while Iran's opposition is fragmented, the various groups have come together. "This is a very important moment in Iranian history, and it is probably time to start asking whether Iran's uprising could become a Berlin Wall moment," Wright said in an interview with CNN's "American Morning."
She added, "It's not just an issue of the sporadic protests once or twice a month... It's also one of the most vibrant and imaginative civil disobedience campaigns anywhere in the world."