Students leave The Evergreen State College campus in Olympia, Wash., after a threat prompted a student alert and evacuation on Thursday, June 1, 2017. (Lisa Pemberton/The Olympian via AP)

OLYMPIA, Wash. - A small college in Washington state closed abruptly Thursday in response to a threat following a recent series of protests that have drawn national attention to student allegations of racism on the progressive campus.

It comes as many defenders of the First Amendment say they see signs that free speech is losing ground as a priority at U.S. colleges and is being used as a political weapon to silence opposing viewpoints.

Law enforcement thought the threat was credible enough to forward to Evergreen State College in Olympia, and school officials decided to close the campus, Sandra Kaiser, Evergreen's vice-president for college relations, told reporters Thursday.

Kaiser did not know the source of the threat or whether it was tied to recent protests at the college.

Officials said on the college website Thursday evening that someone called the Thurston County Communications Center at 10:25 a.m. Thursday claiming to be armed and on the way to campus.

Officials say the call was made from an unknown telephone number to the communications centre's regular business phone line and not their 911 lines.

Officers were "visible and present" on campus Thursday, and school officials were waiting to hear from law enforcement when they could "give the all clear," Kaiser said. On Thursday evening, officials said the campus would remain closed on Friday although officials said a search of campus buildings determined no one was actively posing a threat.

The threat follows protests over a white professor opposing an April event in which organizers asked white students to leave campus for a talk about race issues. It was a reversal from the longstanding annual "Day of Absence," in which minorities traditionally attend programs off campus.

Biology professor Bret Weinstein, who has taught at Evergreen for 15 years, wrote an op-ed piece in the Wall Street Journal saying he was called a racist because he had "challenged coercive segregation by race."

Weinstein said a group encouraging another group to go away was "an act of oppression in and of itself," The News Tribune reported. Evergreen State said participation has always been optional.

"White students have never been required to leave campus, for Day of Absence, or any Evergreen activity," the college said.

Advocates say the effort helps increase social awareness, but critics call it divisive.

Some students called for Weinstein to resign, and conservative media pointed to the furor as an example of intolerance on college campuses, where protests have derailed multiple appearances by controversial figures.

The University of California, Berkeley, was criticized for cancelling an appearance by conservative commentator Ann Coulter in April and another by right-wing provocateur Milo Yiannopoulos in February. It cancelled Coulter's speech amid threats of violence, fearing a repeat of clashes ahead of the Yiannopoulos event.

Berkeley, the birthplace of the U.S. free speech movement in the 1960s, has become a flashpoint for the extreme left and right since Trump's election. It is one of dozens of U.S. campuses where speeches have been disrupted or cancelled by student protests in the past year.

Weinstein told Seattle news station KING-TV that he held a class in a downtown Olympia park May 25 after being told by the college's police chief that "it's not safe for me to be on campus." An administrator confirmed that police advised Weinstein it "might be best to stay off campus for a day or so," the station reported.

Addressing the protests, the college said on its website that demonstrations May 23 and May 24 were nonviolent. It also said: "Everyone on our campus has the right to feel safe. Free speech must be fostered and encouraged. Every faculty member, student, and staff member must have the freedom to speak openly."

A Republican state lawmaker is proposing cutting state funding to Evergreen State after blasting the recent protests. Rep. Matt Manweller said he wants lawmakers to privatize the public school that the Legislature created in 1967, The News Tribune reported.

Some Democrats, who control the state House, have rejected the idea.

Evergreen is a "great institution" that should continue getting state money, Rep. Beth Doglio, an Olympia Democrat, told the newspaper. "Students there are working to make it a more inclusive, diverse campus."

News from © The Associated Press, 2017