TEHRAN, Iran (AP) _ Police have closed the main office of Iran's largest student organization in an ongoing crackdown by religious hard-liners on popular reformist movements, a student leader said Wednesday.

The Office for Fostering Unity headquarters was raided and closed by police late Monday following angry exchanges between student leaders and a splinter group within the organization, said Akbar Atri, one of the mainstream group's leaders.

Some students said the exchanges descended into violence.

Atri denied this, but said police and vigilantes loyal to the hardline faction within Iran's ruling establishment raided the office, bashed students and arrested more than 36 mainstream members of the student body before freeing them.

Police gave no explanation for the office's closure, Atri said.

Atri said hard-liners tried to destroy the reformist student movement by sending in ``infiltrators'' and creating dissent.

Hard-liners opposed to President Mohammad Khatami's democratic reform movement have closed dozens of pro-reform newspapers, intimidated activists and ordered the jailing of legislators.

Khatami, a mid-ranking cleric, has led a popular movement for an easing of social laws that impose restrictions on Iranians. Student groups have been among Khatami's strongest backers.

But staunch opposition by hardline opponents has frustrated meaningful reform.

Differences began occurring inside the student organization after one of the leaders, Mahdi Tabatabaei, began opposing group leader Ali Afshari and other top aides.