Police in the US city of New York have raided Columbia University to remove people protesting Israel's attacks on Gaza.

On Tuesday night, police officers climbed into a building through a window. The building was occupied by protesters.

Earlier in the day, police told reporters that once-peaceful protests were being exploited by professional outside agitators. They expressed their readiness to cooperate with the university if it asked for help.

Students have put up tents on the university's campus to protest the Israeli attacks. Some demonstrators took over the building on Tuesday, one day after the university made an announcement that it would suspend students who defied a deadline for vacating the encampment.

On April 18, police arrested more than 100 protesters at Columbia University who refused to disperse. Since then, demonstrations have spread to other universities across the US.