New York City police officers entered the grounds of Columbia University on Tuesday night to arrest and disperse pro-Palestinian protesters who took over a campus building nearly 24 hours earlier and have been encamped on the campus for two weeks.

TV images showed police entering the university in Upper Manhattan, which has been the focal point of student protests that have spread to dozens of schools across the U.S.

In a letter, Columbia University President Nemat Minouche Shafik requested the New York police to help clear the protest sites and retain a presence on campus through at least May 17 to maintain order and ensure encampments are not reestablished.

The Columbia University chapter of the American Association of University Professors criticized the university president and the board of trustees in a statement on Tuesday night.

"Columbia faculty have spent the day offering our help to defuse the situation on Columbia's campus and have been rebuffed or ignored," the statement said.

It criticized university leadership for bringing in the police, allegedly without consulting faculty.

"Armed police entering our campus places students and everyone else on campus at risk," the statement said.

(With input from agencies)