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.

Hundreds of helmeted police descended onto the campus of the University of California at Los Angeles after darkness fell on Wednesday, preparing to clear out a pro-Palestinian protest camp attacked the previous night by pro-Israel supporters.

The impending crackdown at UCLA is 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, school administrators and law enforcement.

Starting around sunset, officers in tactical gear began filing onto the UCLA campus adjacent to a complex of tents occupied by throngs of demonstrators. Some protesters were seen donning hard hats, goggles and respirator masks in anticipation of the raid 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.

The demonstrators, many wearing the traditional Palestinian keffiyeh scarves, also chanted, "Disclose, divest, we will not stop. We will not rest," and "Free free Palestine."

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."

But police officers stood by on the periphery of the tents for hours - presumably to let crowds of onlookers thin out - awaiting word from commanders to remove barricades and march into the encampment to arrest occupants who refused to leave.

Prior to moving in, police with a loudspeaker urged the demonstrators to clear the protest area in a grassy plaza between the landmark twin-tower auditorium Royce Hall and the main undergraduate library.

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.