Mumford and Sons vowed that they would not return to Sweden’s Bravalla music festival after learning about reports that 17 women were sexually assaulted during the weekend event, held in the southern city of Norrkoping.

Authorities received five reports of rape and 12 of sexual assault during Sweden’s biggest festival.

“We’re appalled to hear what happened at the Bravalla Festival last weekend,” the band wrote on Facebook. “Festivals are a celebration of music and people, a place to let go and feel safe doing so. We’re gutted by these hideous reports.”

They continued, “We won’t play at this festival again until we’ve had assurances from the police and organizers that they’re doing something to combat what appears to be a disgustingly high rate of reported sexual violence.”

Mumford and Sons performed at the festival over the weekend, along with Wiz Khalifa, The 1975 and others.

In another incident, police received 35 reports of alleged assault from young women attending the Putte i Parken festival in Karlstad, according to the Associated Press. Swedish police have reportedly identified seven young males suspected of carrying out the attacks. Karlstad Police Inspector Leif Nystrom said there were no reports of rape, only groping.

Most of the victims were under 18 years old, and three of the girls were under the age of 15.