McGill University says a protest that culminated in the arrest of 15 people Thursday was a "troubling" event in a series of escalating incidents that have taken place since pro-Palestinian demonstrators set up an encampment on campus more than a month ago.

The university says in a statement that protesters blockaded several doors during Thursday's demonstration, and damaged furniture and yelled threats, forcing some staff members to shelter in place.

The school said it supports the right to freedom of expression but condemns "the use of intimidating, aggressive, harassing or illegal tactics such as those seen yesterday."

Police said 13 people were arrested for breaking and entering and two for obstructing police work after a protest was forcefully dispersed on campus.

The arrests came after demonstrators occupied the main administration building on McGill's downtown campus, and officers in riot gear launched chemical irritants.

Pro-Palestinian protesters set up camp on McGill's lower field in late April, demanding the university pull its investments tied to Israel's military and sever relationships with Israeli academic institutions.

A spokesperson for Montreal police acknowledged officers used tear gas and shields to disperse protesters who were outside.

Véronique Dubuc said protesters threw objects and rocks at the officers.