Hundreds of Iranian students expressed their anger over a crackdown on activists and protested Sunday at Tehran University, the second such demonstration in less than a week, witnesses and state radio said.

One witness, Mehdi Arabshahi, said the campus protest lasted more than two hours as students rallied against President Mahmoud Ahmadinejad's hardline administration.

"Students chanted against policies by Ahmadinejad's administration, which is imposing pressures on the universities and detaining activists," Arabshahi said.

Another witness, Abbas Kazemi, said the protesters also called out anti-war slogans aimed at the United States and Israel.

He said students from other universities joined in the protest and broke one of the university's gates. But, Kazemi said, there were no clashes with police and no one was detained.

Tehran state-run radio in a news brief confirmed that students held a protest at Tehran University, saying the students chanted slogans against officials. It also said a group of non-students entered the university after breaking one of the gates but provided no other details. The media was not allowed to enter the university.

The university and its surrounding neighborhood was calm after the gathering and welders were repairing the broken gate.

The protests were held to mark National Day of Students, which has been celebrated since 1953 when three Iranian students were shot to death by police during a protest of a visit by then U.S. Vice President Richard Nixon to Tehran.

The demonstrations also came as state TV announced Sunday that Iran's Intelligence Ministry had detained a group of activists it described as hecklers who planned to stage an illegal gathering at Tehran University.

Quoting a statement by the ministry, the TV report said the activists, who came from various cities, entered the university using fake identification cards before they were detained.

The report said intelligence officers confiscated concussion grenades, illegal books, pamphlets and alcoholic beverages from the detainees.

It did not elaborate on number of detainees or say when the arrests took place.

Last week, a group of left-wing students said 33 students and activists including four women were detained Tuesday after they staged a protest on the Tehran University campus.

Students were once the main power base of Iran's reform movement but have faced intense pressure in recent years from Ahmadinejad's hard-line government, making anti-government protests rare.

Since October, students from different universities have staged occasional protests over educational shortages, the firings of liberal teachers and dentition of activists.

About 100 students staged a rare protest in October against Ahmadinejad, calling him a "dictator" as he gave a speech at Tehran University marking the beginning of the academic year.

The president faced a similar outburst during a speech in December 2006 when students at Amir Kabir Technical University called him a dictator and burned his picture.

Iran's reform movement peaked in the late 1990s after former reformist President Mohammad Khatami was elected and his supporters swept parliament. But during that time, hard-liners who control the judiciary, security forces and powerful unelected bodies in the government, stymied attempts to ease social and political restrictions.

Reformists — who want to loosen Iran's social and political restrictions and favor better relations with the U.S. — were further demoralized and divided after the 2005 election that brought Ahmadinejad to power.

In recent months, dissenters have witnessed an increasing crackdown in Iran, and hundreds have been rounded up on accusations of threatening the Iranian system. Numerous pro-reform newspapers have been shut down and those that remain have been muted in their criticism fearing closure.

At universities, pro-reform students have been marginalized and now only hold low-level meetings and occasional demonstrations, usually to demand better school facilities or the release of detained colleagues. At the same time, pro-government student groups have grown more powerful.

Some dissenters blame the crackdown on the regime's fear of a U.S. effort to undermine it as tensions over Iran's nuclear program intensify. Others say the intent is simply to contain discontent fueled by a faltering economy.

Ahmadinejad's popularity at home has fallen since he was elected, with critics saying he has failed to fix the economy and has hurt Iran's image internationally.

Conservatives who once supported the president have increasingly joined in the criticism, saying he needs to pay more attention to domestic issues and his inflammatory rhetoric has needlessly stoked tensions with the West.