Hundreds of helmeted police muscled their way into a central plaza of the University of California at Los Angeles early on Thursday in a move to disperse a pro-Palestinian protest camp attacked the previous night by pro-Israel supporters.

The pre-dawn police crackdown at UCLA marked the latest flashpoint for mounting tensions on U.S. college campuses, where protests over Israel's conduct of the war in Gaza have led to student clashes with each other and law enforcement.

Starting around sunset on Wednesday, officers in tactical gear began filing onto the UCLA campus adjacent to a complex of tents occupied by throngs of demonstrators, live footage from the scene showed.

Local television station KABC-TV estimated 300 to 500 were hunkered down inside the camp, while around 2,000 more had gathered outside the barricades in support.

But the assembled police stood by on the periphery of the tents for hours before finally starting to force their way into the encampment around 3:15 a.m. PDT (1015 GMT) to arrest occupants who refused to leave. The raid was led by a phalanx of California Highway Patrol officers carrying shields and batons.

Demonstrators, some carrying makeshift shields and umbrellas, sought to block the officers' advance by their sheer numbers, while shouting, "push them back" and flashing bright lights in the eyes of the police.

Some protesters had been seen donning hard hats, goggles and respirator masks in anticipation of the siege a day after the university declared the encampment unlawful.

Hundreds of other pro-Palestinian activists who assembled outside the tent city jeered police with shouts of "shame on you", some banging on drums and waving Palestinian flags, as officers marched onto the campus grounds. Many wore the traditional Palestinian scarves called keffiyehs.

A much smaller group of demonstrators waving Israeli flags urged on the police to shut down the encampment, yelling, "Hey hey, ho-ho, the occupation has got to go".

Prior to moving in, police urged demonstrators in repeated loudspeaker announcements to clear the protest zone, occupying a plaza about the size of a football field between the landmark twin-tower auditorium Royce Hall and the main undergraduate library.

VIOLENT CLASH PRECEDES CRACKDOWN

UCLA had canceled classes for the day following a violent clash between the encampment's occupants and a group of masked counter-demonstrators who mounted a surprise assault late Tuesday night on the tent city.

The occupants of the outdoor protest camp, set up last week, had remained otherwise peaceful before the melee, in which both sides traded blows and doused each other with pepper spray.

Members of the pro-Palestinian group said fireworks were thrown at them and they were beaten with bats and sticks. University officials blamed the disturbance on "instigators" and vowed an investigation.

The confrontation went on for two or three hours into early Wednesday morning before police restored order. A spokesperson for California Governor Gavin Newsom later criticized the "limited and delayed campus law enforcement response" to the unrest as "unacceptable".

As the much-expanded police force entered the campus on Wednesday night to clear the encampment, some of the protesters were heard yelling at them, "Where were you yesterday?"

UCLA officials said the campus, which enrolls nearly 52,000 students, including undergraduates and graduate scholars, would remain shuttered except for limited operations on Thursday and Friday.

Wednesday night's police action came a day after police in New York City arrested pro-Palestinian activists who occupied a building at Columbia University and removed a tent city from the campus of the Ivy League school.

Police arrested a total of about 300 people at Columbia and City College of New York, Mayor Eric Adams said. Many of those arrested were charged with trespassing and criminal mischief.

The clashes at UCLA and in New York were part of the biggest outpouring of U.S. student activism since the anti-racism rallies and marches of 2020.

Ninety pro-Palestinian demonstrators - students and outsiders - were arrested at Dartmouth University in New Hampshire on Wednesday, the Hanover Police Department said. They were charged with criminal trespass and resisting arrest.

The protests follow the Oct. 7 attack on southern Israel by Hamas militants from the Gaza Strip and the ensuing Israeli offensive on the Palestinian enclave.

Students have rallied or set up tent encampments at dozens of schools across the U.S. in recent days, calling for an immediate ceasefire in Gaza and demanding schools divest from companies that support Israel's government. Many of the schools have called in police to quell the protests.

The demonstrations across the country have been met with counter-protesters accusing them of fomenting anti-Jewish hatred. The pro-Palestinian side, including Jews opposed to Israeli actions in Gaza, say they are being unfairly branded as antisemitic for criticizing Israel's government and expressing support for human rights.

The issue has taken on political overtones in the run-up to the U.S. presidential election in November, with Republicans accusing some university administrators of turning a blind eye to antisemitic rhetoric and harassment.