Tehran, Iran (CNN) -- An Iranian national security official has called for demonstrators to be arrested following deadly weekend anti-government protests in Tehran. Soon afterward, an opposition Web site reported a wave of arrests.
"The undignified and disruptive behavior of the rioters is no longer tolerable for our people, since they have brought undignified behaviors to new heights by offending sanctities and values held dear in Islam and Iran," Naghavi Hosseini, a member of the Parliamentary National Security and Foreign Policy Commission, told state-run IRNA.
"The Nation's Judiciary must swiftly arrest the rioters who committed those crimes."
An opposition Web site, NoroozNews, said government officials took several activists into custody Monday, including some close advisors to opposition leader and former presidential candidate Mir Hossein Mousavi.
The government did not immediately respond to the report.
Meanwhile, the death toll from Sunday's anti-government protests in Tehran stood at eight, the country's Supreme National Security Council said.
With tight restrictions on international media, CNN could not independently verify the casualties that were reported Monday by state-run Press TV.
The Press TV report did not say how many others were arrested. But earlier, Iran's Deputy Police Chief Ahmad Reza Radan said on state television station IRINN that more than 300 were taken into custody.
Opposition Web site Rahesabz.net reported the arrests of at least three figures from the reformist movement and also noted that Tehran's text messaging system had slowed to a crawl with the outbreak in violence.
The toll was the result of clashes that broke out between demonstrators and security forces as large crowds gathered for Ashura, a major religious observance that marks the death of Imam Hussein, grandson of Prophet Mohammed, as a martyr.
Some demonstrators over the weekend compared Ayatollah Khamenei -- the supreme leader of the nation's hardline Islamic government -- to Yazid, the caliph who killed Imam Hussein.
Radan said those killed included one person who fell off a bridge and two others who were killed in a car accident during the protests.
One of the victims was killed by a bullet, Radan said. But "considering the fact that the police did not use firearms, this incident is extremely suspicious, and is being investigated," he added.
Mousavi's Web site reported that his nephew, Seyed Ali Mousavi, was killed in the demonstrations by a shot to the heart.
Press TV late Sunday quoted unnamed police officials as identifying one of the dead as "Seyyed Ali Mousavi" but it did not mention the elder Mousavi or any relationship between the two men.
Tehran Police Chief Azizollah Rajabzadeh denied that any protesters were killed by security forces. Police did not fire any shots in Tehran, "and security forces were not in possession of firearms," Rajabzadeh told the semi-official news agency ISNA.
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.
Since the disputed presidential elections in June, protesters have turned public gatherings into rallies against President Mahmoud Ahmadinejad, who was declared the overwhelming winner of the race.
CNN's Reza Sayah, an Iran native who covers the region, has called recent events 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."
The unrest Sunday followed day-long clashes between the two sides in the streets of Tehran on Saturday.
On Saturday evening, a pro-government mob barged into a mosque where former president and reformist leader Mohammad Khatami was speaking.
The dozens-strong group forced Khatami to end his remarks abruptly when it interrupted the gathering at Jamaran mosque.
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.
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."
-- CNN's Josh Levs contributed to this report