TEHRAN, Iran - Hundreds of students at Tehran University renewed antigovernment demonstrations for a second week yesterday, accusing authorities of fabricating images of demonstrators burning photos of the Islamic Republic's revered founder.

They said authorities were using images showing the burning photos of Ayatollah Ruhollah Khomeini as a pretext to crack down on their protests, which have helped revitalize the pro-reform movement.

State television has repeatedly shown images, ostensibly taken during student-led protests on last Monday, of unidentified hands burning and tearing up pictures of Ayatollah Ruhollah Khomeini.

The elite Revolutionary Guard, the country's most powerful military force, called for punishment of those responsible. Under the law, insults to the late or current supreme leader can lead to two years in prison.

Government supporters, including hard-line clerics, rallied on Friday and Saturday to denounce those who burned photos of the clerical leaders. Tens of thousands turned out Saturday.

Mohammad Nourizad, a filmmaker and activist, said no matter who was behind the destruction of photos of Khomeini, the offense paled in insignificance when compared with the killings of protesters. He said the government was using the issue as a "childish tactic" against its opponents.

Iran's opposition says 72 protesters were killed in the weeks after the disputed June presidential election. The government puts the number of dead at 30.

Student activists said authorities were trying to discredit them just as they begin to put up a new, powerful challenge to the regime.

The opposition's leaders have struggled to dent the power of President Mahmoud Ahmadinejad and the current clerical supreme leader, Ayatollah Ali Khamenei.

Students at Tehran University played a major role in street demonstrations in support of the 1979 Islamic Revolution that toppled to pro-U.S. shah and brought Iran's clerical rulers to power.

Reformists contend that Ahmadinejad was reelected by massive vote fraud, a belief that brought hundreds of thousands of protesters into the streets at the height of postelection unrest.

Former President Mohammad Khatami, a prominent opposition voice, also said students were not behind the destruction of the photos.

"Do not use the Imam to justify a harsher approach against those you do not like," he was quoted as saying on a pro-reform Web site.

Video circulated widely on the Internet on the day of last week's protests also showed photos of Khamenei and Ahmadinejad being burned, as well as one photo of Khamenei and Khomeini side by side. The faces of those burning the pictures could not be seen and chants against the government were heard in the background.

Khamenei, who has the final say on all state matters, appealed for calm, but he suggested the opposition was creating a hostile environment.

"Some have turned the election campaign into a campaign against the entire system," he said without naming any opposition leaders. "We call on those who are angry to remain calm."

Opposition leader Mir Hossein Mousavi has said his supporters love Khomeini and would not take actions that insulted him.

During yesterday's demonstration, dozens of police ringed Tehran University, but they did not enter the campus.