Dozens of helmeted police flooded Columbia University's campus in the heart of New York City on Tuesday to evict a building occupied by pro-Palestinian student protesters and detain demonstrators.
Police climbed into Hamilton Hall via a second floor window they reached from a laddered truck, before leading handcuffed students out of the building into police vans.
The hall had been occupied at dawn by demonstrators who vowed they would fight any eviction, as they protested the soaring death toll from Israel's war with Hamas in the Gaza Strip.
The action came as university administrators around the United States have struggled for weeks to contain pro-Palestinian demonstrations on dozens of campuses.
In a letter addressed to the New York Police Department, Columbia University president Minouche Shafik said that the occupation of the school building was being led by "individuals who are not affiliated with the University" and asked "NYPD's help to clear all individuals from Hamilton Hall and all campus encampments."
She also asked the police to remain on campus through at least May 17, "to ensure encampments are not reestablished." Commencement is scheduled for May 15.
Writing on Instagram, the protesters slammed Shafik's statement, saying "her use of the words 'care' and 'safety' are nothing short of horrifying."
The weeks of demonstrations -- the most sweeping and prolonged unrest to rock US college campuses since the Vietnam war protests of the 1960s and 70s -- have already led to several hundred arrests of students and other activists.
Earlier, protesters at Columbia were seen using ropes to hoist crates of supplies up to the building's second floor, apparently signaling the students had planned to hunker down.
President Joe Biden's White House had sharply criticized the seizure of Hamilton Hall, with a spokesman saying it was "absolutely the wrong approach."
"That is not an example of peaceful protest," the spokesman added.
Former US president Donald Trump lamented the "anti-Semitism that's just pervading our country," and slammed Biden, his rival in the November presidential election for inaction.
"Biden has to do something. Biden is supposed to be the voice of our country and... it's a voice that nobody's heard," Trump said Tuesday evening on Fox News.
A nationwide movement
The protests, with Columbia at their epicentre, have posed a challenge to university administrators trying to balance free speech rights with complaints that the rallies have veered into anti-Semitism and hate.
The unrest has swept through US higher education institutions like wildfire, with many student protesters erecting tent encampments on campuses from coast to coast.
At Columbia, demonstrators have vowed to remain until their demands are met, including that the school divest all financial holdings linked to Israel.
The university has rejected the demand. Columbia has warned that students occupying the building face expulsion.
In one of the newest clashes, at the University of North Carolina at Chapel Hill, police moved in Tuesday to clear one encampment, detaining some protesters in a tense showdown.
Meanwhile at northern California's Cal Poly Humboldt, a week-long occupation was brought to a dramatic end early Tuesday when police moved in to arrest nearly three dozen protesters who had seized buildings and forced the closure of the campus.
In Oregon, Portland State University's campus was closed Tuesday "due to an ongoing incident" in the library, college authorities said, after local media reported around 50 protesters had broken into the building a day earlier.
And Brown University reached an agreement in which student protesters will remove their encampment in exchange for the institution holding a vote on divesting from Israel -- a major concession from an elite American university during the protests.
Footage of police in riot gear summoned at various colleges has been viewed around the world.
UN human rights chief Volker Turk voiced concern at the heavy-handed steps taken to disperse the campus protests, saying "freedom of expression and the right to peaceful assembly are fundamental to society."
He added that "incitement to violence or hatred on grounds of identity or viewpoints -- whether real or assumed -- must be strongly repudiated."
Shafik said many Jewish students had fled Columbia's campus in fear. "Anti-Semitic language and actions are unacceptable," she said.
The Gaza war started when Hamas militants staged an unprecedented attack on Israel on October 7 that left around 1,170 people dead, mostly civilians, according to an AFP tally of Israeli official figures.
During their attack, militants also seized hostages, 129 of whom Israel estimates remain in Gaza, including 34 whom the military says are dead.
Israel's retaliatory offensive has killed at least 34,535 people in Gaza, mostly women and children, according to the Hamas-run territory's health ministry.