(Reuters) - Pro-Palestinian protests at U.S. universities showed no sign of slowing as they spread coast-to-coast over the weekend and police crackdowns and arrests continued into another week while students vowed to stay in tent encampments until their demands are met.

The students' demands range from a ceasefire in Israel's war with Hamas to calls for universities to stop investing in Israeli enterprises involved with the country's military to an end for U.S. military assistance for Israel.

Pro-Palestinian protests have spread to college campuses across the U.S., stoked by the mass arrest of over 100 people on Columbia University's campus more than a week ago.

The Columbia campus was peaceful on Saturday and there were no reports of arrests of disturbances overnight, a school spokesman told Reuters.

But crackdowns continued at a handful of campuses on Saturday including a lockdown at the University of Southern California (USC) and a heavy police presence. More than 200 people were arrested at a handful of schools including 80 late on Saturday at Washington University in St. Louis. Among those arrested at Washington University was 2024 Green Party presidential candidate Jill Stein.

"They are sending in the riot police and basically creating a riot in an otherwise peaceful demonstration. So this is just shameful," Stein said in a statement.

Washington University said in a statement that those arrested would be charged with trespassing.

On Sunday, dueling demonstrations were set to begin at the University of Southern California, Los Angeles. Outside groups were planning to demonstrate in favor of and against the pro-Palestinian encampments.

Members of the Harriet Tubman Center for Social Justice planned to support students' right to protest.

In opposition, however, a group called Stand With Us will hold a "Stand in Support of Jewish Students" rally to "stand up against hatred and antisemitism."

The nationwide protests have caught the attention of President Joe Biden.

White House national security spokesman John Kirby told ABC News on Sunday that the president knows there are very strong feelings about the war in Gaza.

"He understands that, he respects that and as he has said many times, we certainly respect the right of peaceful protest," Kirby said. "People should have the ability to air their views and to share their perspectives publicly, but it has to be peaceful."

Kirby added that the president condemns antisemitism and condemns hate speech.

At USC, leadership has cancelled the main commencement ceremony after it called off the valedictorian speech by a Muslim student who said she was silenced by anti-Palestinian hatred.

Los Angeles Mayor Karen Bass said on Sunday she believed that cancelling the commencement was a decision "they had to make."

"They were expecting about 65,000 people on campus, and they just did not feel that it was going to be safe," Bass said on CNN's "State of the Union."

(Reporting by Rich McKay in Atlanta; Additional reporting by David Ljunggren in Ottawa; Editing by Mary Milliken and Matthew Lewis)

By Rich McKay