The UN warned Friday against using excessive force against demonstrators and media in the United States and said the deployment of unidentified officers increased the risk of human rights violations.

Responding to questions about violent clashes in the US city of Portland between federal forces and demonstrators protesting against racism and police brutality, a UN spokeswoman stressed that the right to peacefully assemble and protest must be protected.

“Peaceful demonstrations that have been taking place in cities in the US, such as Portland, really must be able to continue,” UN rights office spokeswoman Elizabeth Throssel told reporters in Geneva.

People must be able to demonstrate, and journalists must be able to cover such protests, without “risking arbitrary arrest or detention, being subject to the unnecessary disproportionate or discriminatory use of force or suffering other violations of their rights,” she said.

Protests raged in the US after the killing of George Floyd, an African American man who died at the hands of police in Minneapolis on May 25. Those protests began losing steam earlier this month, before reports emerged of federal officers snatching Portland protestors and taking them away in unmarked vehicles, spurring a fresh wave of demonstrations.

The US Justice Department’s independent watchdog announced Thursday it was launching probes into the use of force by federal agents in Portland.

Throssel said that the reports of unidentified officers making arrests were a particular cause for concern. She noted that such practices could give rise to arbitrary detention and other human rights violations.

“We would stress … that the authorities should ensure that the federal and local security forces deployed are properly and clearly identified and use force only when necessary, proportionate, and in accordance with international standards,” she said. Globally, she added, authorities must ensure that people deployed for law enforcement do not threaten the “use of force to deter peaceful protesters.”