Police in Sweden said they have identified seven young males suspected of sexually assaulting girls and young women at a festival in southern Sweden at the weekend.

Insp Leif Nyström from Karlstad police said on Tuesday they had received 32 reports of alleged assaults by boys or young men at the three-day festival in the city of Karlstad, 190 miles (300km) west of the capital, Stockholm. The youngest alleged victim was 12. The attacks included groping but there were no reports of rape.

Nyström said police had identified the perpetrators but that no one had yet been detained. He declined to give more information about the cases or the suspects’ identities.

Meanwhile, in Norrköping, police told local media they were investigating five cases of alleged rape and more than a dozen suspected sexual assaults at the Bravålla festival in the city, south-west of Stockholm.

After playing in Norrköping, British band Mumford & Sons posted a note on their Facebook site saying they were “appalled ... and gutted by these reports” of rape and sexual assault.

The band said on Tuesday they would not play Bravålla again unless police and organisers could assure them they were “doing something to combat what appears to be a disgustingly high rate of reported sexual violence”.

The Swedish prime minister, Stefan Löfven, described the situation as “totally unacceptable” and said laws on sexual assault would be tightened.

“We are in the process of reviewing them,” he said in a speech at a political seminar. “It’s also important that we continue to ensure that police, prosecutors and other officials are better equipped to investigate such crimes and actually catch the perpetrators.”

Nyström declined to give details of the suspects or comment on reports that the offences in Karlstad were committed by migrants or foreigners, pending the outcome of the investigation.

“We want to catch the suspects because we need to talk to them,” he said. “The number of such cases has increased slightly since last year, but I’m really not sure if this is a common problem at festivals.”

In January, Swedish police faced allegations of a cover-up for failing to inform the public of widespread sexual assaults against teenage girls at a music festival a year ago, which came to light when the Swedish daily Dagens Nyheter reported them following a string of sexual assaults and robberies on New Year’s Eve in Cologne, Germany.

In neighbouring Denmark, where the annual week-long Roskilde rock festival attended by 130,000 people finished on Sunday, police said they had reports of five cases of alleged rape or sexual assault, which officer Carsten Andersen described as “nothing out of the ordinary at such a big event, although every single case is too much”.