Spiralling pro-Palestinian protests that are rocking universities across the United States spread to more campuses on Wednesday (Apr 24), triggering suggestions from a senior Republican leader that the National Guard could be brought in.

The comments from House Speaker Mike Johnson are likely to evoke strong emotions in a country where the 1970 killing by National Guardsmen of unarmed students protesting the Vietnam War lives on in folk memory.

Demonstrations erupted at the University of Southern California on Wednesday, and in Texas, where a tense stand-off developed between students and police in riot gear, with more than 20 people detained.

It was the latest confrontation between law enforcement and students angry at the mounting death toll in Israel's war against Hamas.

The movement began at Columbia University in New York where dozens of arrests were made last week after university authorities called in police to quell an occupation that Jewish students said was threatening and anti-semitic.

Johnson told reporters at Columbia that if the demonstrations were not contained quickly it would be "an appropriate time for the National Guard".

He said he intended to demand US President Joe Biden "take action", and warned that the demonstrations "place a target on the backs of Jewish students in the United States".

White House spokeswoman Karine Jean-Pierre said Biden backed free speech.

"The president believes that free speech, debate and nondiscrimination on college campuses are important," she told reporters.

US ally Israel launched its war in Gaza after the Hamas attack on Oct 7 that left around 1,170 people dead, according to an AFP tally of Israeli official figures.

Student protesters say they are expressing solidarity with Palestinians in Gaza, where the death toll has topped 34,200, according to the Hamas-run health ministry, and are calling on Columbia and other universities to divest from companies with ties to Israel.

The demonstrators - including a number of Jewish students - have disavowed instances of anti-semitism.

But pro-Israel supporters and others worried about campus safety, have pointed to anti-semitic incidents and argued that campuses are encouraging intimidation and hate speech.