Tensions over strong opinions about Israel's war in Gaza are spreading at some universities around the United States.

On Monday, Columbia University in New York City canceled in-person classes.

Pro-Palestinian demonstrations, including occupations, have been taking place on campus for days.

Last week, police arrested more than 100 demonstrators at Columbia.

Also on Monday, police in New Haven, Connecticut, arrested about 45 protesters at Yale University.

Officials said the students refused orders to leave an area they were occupying.

Columbia and Yale are two of the so-called "Ivy League" universities considered among the nation's top schools.

Pro-Palestinian demonstrations also are taking place on other campuses around the country, including the University of Michigan, the Massachusetts Institute of Technology, and the University of North Carolina.

Columbia University President Minouche Shafik said in a statement Monday that she was "deeply saddened" by what was happening at the school.

"I am announcing that all classes will be held virtually on Monday," Shafik said, adding that she hoped the move would ease tensions.