Mumford and Sons are boycotting a Swedish music festival they headlined at the weekend after several reports of sexual assaults.

Five rapes and more than a dozen suspected sexual assaults were reported at the Bravalla Festival in the city from June 29 to July 2.

The band said they were "gutted" to hear of the reports and vowed to not play there again until security had improved.

Organisers of the festival reportedly handed out bracelets saying "don't grope".

Swedish Prime Minister Stefan Lofven described the situation as "totally unacceptable" and said laws on sexual assault would be tightened.