The unprecedented intervention by the Geneva-based United Nations body adds to international calls for Hong Kong to set up an independent investigation into the anti-government protests that have rocked the city for more than two months.

“The UN Human Rights Office has reviewed credible evidence of law enforcement officials employing less-lethal weapons in ways that are prohibited by international norms and standards,” office spokesman Rupert Colville said in a statement on Tuesday.

“Officials can be seen firing tear gas canisters into crowded, enclosed areas and directly at individual protesters on multiple occasions, creating a considerable risk of death or serious injury.”

The office urged the Hong Kong authorities to investigate the incidents immediately, “to ensure security personnel comply with the rules of engagement, and where necessary, amend the rules of engagement for law enforcement officials in response to protests where these may not conform with international standards”.

It urged the authorities to act with restraint to ensure that the rights of those expressing their views peacefully were respected and protected, and that police were “proportionate” in their response to any violence.

In the statement, UN High Commissioner for Human Rights Michelle Bachelet condemned “any form of violence or destruction of property” and urged demonstrators to express their views in a peaceful way.

Acknowledging Hong Kong Chief Executive Carrie Lam Cheng Yuet-ngor’s commitment to “engage as widely as possible” and to “listen to the grievances of the people of Hong Kong”, Bachelet called on the authorities and the people of Hong Kong to engage in an open and inclusive dialogue to resolve all issues peacefully.

“This is the only sure way to achieve long-term political stability and public security by creating channels for people to participate in public affairs and decisions affecting their lives,” she said.

Lam said earlier on Tuesday that dialogue would not start unless chaos on the streets stopped.