Several media outlets in Iran reported, albeit in a restricted and censured fashion, that there has been rioting on several university campuses in Tehran for the past four days. The reformist Internet daily Rooz reported that over 500 members of riot-control units have besieged the Tehran University campus, and that there have been clashes between demonstrating students and Basij and police forces.
The riots broke out following a student protest over what appeared to be a purge of the academic faculty of Tehran University. This coincided with the marking of the "Second of Khordad," the day of the Persian month of Khordad on which Mohammad Khatami was first elected president of Iran (May 23, 1997). 
During the riots, eight student leaders were arrested, and, according to eyewitnesses quoted in Rooz, 25 of those under siege in the campus were wounded, five of them severely. Eyewitnesses reported that students were chanting anti-regime slogans, such as "We don't want nuclear energy" and "Forget Palestine - think of us."
The eyewitnesses also reported that Iranian security forces fired live bullets, and that shots were fired at homes outside the university. One of the students told Rooz: "The university campus is on fire, raids are being conducted throughout the campus, and the students are in fear and anxiety... Gunfire is heard from all directions... There is blood everywhere."  The university's telephone lines were reported to have been cut.
According to other eyewitnesses, "police riot-control units entered the campus with helmets, shields, and clubs, and beat students so severely that many can't even walk." A campus security guard told a Rooz reporter: "We were told that we were permitted to use violence against the students, but not to hit them on their heads or their faces, in order to avoid leaving marks. We were told not to be respectful towards any student, unless he is a member of the Basij student union."
One of the students said: "They are sending more riot-control forces [into the campus]. I estimate that they are about 3,000 strong... There is also an intensive presence of Ansar-e Hizbullah forces in vehicles or on motorcycles. They have also brought in several fire trucks [to disperse the students]..."  One of the reporters said: "Reporters who came to cover the events were stopped by university security guards, and none were permitted to enter [the campus]." 
Local police claim that only 100 students were involved in the demonstrations, but according to eyewitnesses quoted by Rooz, the riots involved some 3,000 of the 4,000 students attending the main campus, and another 2,000 from the law and political science campus. 
The ultra-conservative daily Kayhan, which is close to Iran's Supreme Leader Ali Khamenei, called the student leaders "American representatives of the [U.S.] Congress in Tehran University," and reported that "yesterday afternoon, illegal forces demonstrated in the [university] classrooms after several faculty members were forced to retire." According to Kayhan, the demonstration organizers are not even students but are from outside the university. 
Morteza Talai, commander of the Tehran Metropolitan Police, told the Iranian Students News Agency (ISNA) that "at 9:30 PM, 100 students gathered at the campus gates, and 20 or 30 of them started throwing stones, sticks and firebombs at homes in the area." The report continued: "[Talai said that] the police reacted with restraint, and, until 5:30 AM, made efforts to curb the demonstrators throwing the firebombs... but [the students] paid no heed... Only in the morning did the police raid [the campus], and by 7:00 AM, it had made arrests and cleared the area, with the help of municipal forces... During this activity, three students were injured while attempting to climb onto the roof of the dormitory building."
Iran Focus Demonstration Photos 
 The "Second of Khordad" is the name of Iran's reform movement, which in recent years has been severely suppressed by Iran's conservatives; today it has no political representation.
 ISNA, May 25, 2006: http://www.isna.ir/Main/NewsView.aspx?ID=News-723636&Lang=P
Rooz, May 25, 2006: http://r0ozonline.com/01newsstory/015805.shtml
 Iran Focus, May 23, 2006: http://www.iranfocus.com/modules/news/article.php?storyid=7312