Following a demonstration in Yemen Friday, Amnesty International reported that Houthi authorities arrested an “alarming” number of people. The demonstration was held to commemorate the anniversary of Yemen’s September Revolution, and those taking part were said to be peacefully “exercising their right to freedom of assembly.”

During the demonstration, which remembered the establishment of the Yemen Arab Republic in 1962, protesters in Sana’a, Ibb and Houdeidah took the Yemeni Republic flags out onto the streets in celebration. However, according to reports given to Amnesty International, some demonstrators were attacked by de facto Houthi authorities, who “violently confiscated their flags.” One Yemeni lawyer reported to Amnesty International that Houthi supporters shouted slogans and “threw rocks” at demonstrators.

Amnesty International condemned the actions of the Houthi authorities in response to the peaceful protest. The human rights organisation, which has been recording the Houthi authorities’ “repressive tactics to suppress the right to freedom of expression” since 2015, is calling for all those arrested to be released “immediately and unconditionally.” In a statement regarding the incident, Grazia Careccia, Amnesty International’s Deputy Regional Director for the Middle East and North Africa, commented:

It is outrageous that demonstrators commemorating a national historical moment found themselves attacked, arrested, and facing charges simply because they were waving flags. This repressive crackdown further illustrates the lengths to which Huthi de facto authorities are prepared to go to in order to stifle free expression in areas under their control.

The conflict in Yemen has continued for eight years between the Houthi authorities and the Saudi and UAE-led coalition. It has resulted in widespread civilian harm and many violations of international human rights. Currently, according to the UN, 80 percent of the population is in need of humanitarian aid.