Hong Kong police on Sunday arrested several figures from the pro-democracy movement, including an opposition party leader, who was released shortly afterwards, on the 34th anniversary of the Tiananmen Square massacre in Beijing.

Police deployed en masse this weekend around Victoria Park, in the Causeway Bay shopping district, where thousands of people annually hold a candlelight vigil for the victims of June 4, 1989.

Police arrested Chan Po-ying, a leader of the League of Social Democrats, and loaded him into a van with a candle and flowers. Her party indicated she was released two hours later.

Alexandra Wong, a 67-year-old activist known as “Grandma Wong” as she waved a bouquet of flowers in the air, and journalist and former president of the Hong Kong Journalists Association, Mak Yin-ting, were also arrested.

Another woman was also detained after shouting “Sail hoist! Cry on 4/6!”, referring to the date of the democratic uprising Beijing suppressed with blood.

Hong Kong police said they had detained 23 people, ranging from 20 to 74, for “disturbing the peace”.

The day before, the police had already arrested four people for “disorderly behavior in public places” and another four for “disturbing public order”.

The United Nations High Commissioner for Human Rights, Volker Türk, expressed concern after learning of the arrests, calling in a tweet to “release anyone arrested for exercising their freedom of expression and peaceful assembly”.