Spiralling pro-Palestinian protests that are rocking universities across the United States have spread to more campuses, 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 on Wednesday at the University of Southern California and in Texas, where a tense standoff developed between students and police in riot gear, with more than 20 people detained.

It was the latest confrontation between law enforcement and students protesting against Israel’s war on Gaza.

The movement began at Columbia University in New York City, where dozens of arrests were made last week after university authorities called in police to quell an occupation.

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 that 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.

Student protesters say they are expressing solidarity with Palestinians in Gaza, where the death toll has topped 34,300, according to the Palestinian Health Ministry.

Demonstrators are calling on Columbia and other universities to divest from companies with ties to Israel.

The protesters – including a number of Jewish students – have disavowed instances of anti-Semitism at the demonstrations.

Pro-Israel supporters have pointed to anti-Semitic incidents and argued that campuses are encouraging intimidation and hate speech.