The United Nations criticised the “arbitrary detention” of over 1,800 individuals in Russia for opposing the country’s invasion of Ukraine on Friday, and called for their immediate release.

“Arresting persons for expressing their rights to freedom of speech or peaceful assembly is an arbitrary loss of liberty,” UN rights spokesperson Ravina Shamdasani told reporters, adding that “all those unfairly detained” should be released “immediately.”

Marina Litvinovich, a Moscow-based opposition activist who used social media to call for anti-war rallies in many Russian towns, was among those arrested, Reuters reported.

On Thursday, British Prime Minister Boris Johnson said that all Russian banks’ assets will be frozen, thereby shutting them off from Europe’s largest economy. Protests against Russia were held in a number of Western European cities, including London, Dublin, and Edinburgh, as well as Paris and Berlin.