MUMFORD AND SONS are boycotting a Swedish music festival they headlined at the weekend after dozens of reported sexual assaults.

The band said they were "gutted" to hear of reports of five rapes and more than a dozen suspected sexual assaults at the Bravalla Festival in the city, south-west of Stockholm, that took place from June 29 to July 2.

READ MORE: Man decapitated girlfriend's alleged rapist with machete

In a post on their official Facebook page which was signed by all band members, they vowed not to play it again until security had improved.

It read: "We're appalled to hear what happened at the Bravalla Festival last weekend.

"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.

"We won't play at this festival again until we've had assurances from the police and organisers that they're doing something to combat what appears to be a disgustingly high rate of reported sexual violence."

READ MORE: Man decapitated girlfriend's alleged rapist with machete

The Associated Press reports that police at the Bravalla festival gave out bracelets saying "don't grope".

Also headlining at the three-day festival were Macklemore and Ryan Lewis, Rammstein and Jack Black's band Tenacious D.

Bravalla was one of two Swedish festivals which suffered a high rate of alleged sexual assaults last weekend.

Free festival Putte i Parken in the city of Karlstad, 190 miles west of the capital, had 32 reports of attacks by boys or young men. The youngest alleged victim was 12.

READ MORE: Man decapitated girlfriend's alleged rapist with machete

Police have identified seven young men they wanted to question.

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