A strike by university students in Puerto Rico has begun in the wake of the imposition of an $800 (?513) annual tuition fee and ill feeling about the presence of police on campus.

Police took action at the state-run University of Puerto Rico following a two-day blockade by students, reported by Times ÖйúAƬ last week, which was marked by clashes with private security guards hired by the university.

Superintendent Jos¨¦ Figueroa Sancha said the police had moved in at the request of university president Jos¨¦ Ram¨®n de la Torre and would remain indefinitely to "guarantee the rights of those willing to go to class" and to "prevent crimes within the university".

The university's decree that further protests must be confined to designated areas outside the main university campus has elicited anger. Students are also dismayed by a Puerto Rico Supreme Court ruling stating that they do not have the right to strike.

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The unrest follows a two-month student strike earlier this year over plans for the introduction of tuition fees and cuts to meet the institution's significant budget shortfall.

A committee of law students urged their peers not to enter any of the university's 11 campuses until the police withdrew, "otherwise we will have condoned the death of our non-confrontation policy and of our university's autonomy".

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?rika Font¨¢nez Torres, an associate professor at the university's School of Law, also condemned the presence of police on campus.

"What else will this administration do to...destroy our university? Enough," she writes in her blog.

Another associate professor in law at Puerto Rico, Hiram Mel¨¦ndez Juarbe, said the institution was "at a crossroads" that could determine whether it "continues to exist as a university or perishes in the attempt".

But an assembly of academics urged both sides to declare a truce.

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It said the university must not "be forced to choose between the administration's intransigence or the students' intransigence...What is at stake here is nothing less than the survival of our university."

paul.jump@tsleducation.com.