Free Palestine campaigners disrupted a speech by defence minister Ruben Brekelmans at the University of Amsterdam on Wednesday evening, causing the minister to break off his lecture for 15 minutes.

The demonstrators, who were outside the room where Brekelmans was giving his talk, chanted and banged on windows in an effort to prevent him from being heard.

Brekelmans had been invited by student organisation Room for Discussion to be interviewed in front of an audience.

The police were called to check out the protest but did not intervene.

University chairwoman Edith Hooge said the disruption was “unacceptable.”

“Security guards were hit, those present were intimidated, and a conversation organised by students became impossible,” she said, adding that the university will make a formal police complaint about the protests.

A lecture by Brekelmans’ predecessor Kajsa Ollongren was cancelled last year on security grounds, while an interview with mayor Femke Halsema was moved to her official residence.

“There should be free debate at a university and room for every opinion,” the mayor said in a reaction to Wednesday’s protest. “This disruption is scandalous and goes against the exchange of free academic ideas.”

Dutch universities were hit by a string of protests by pro-Palestine campaigners last year, several of which degenerated into riots.