A 15-year-old boy has been charged with assault at a music festival in Stockholm, where police have been accused of covering up allegations of multiple sexual assaults.

On Monday (11 January), police in Stockholm revealed that there had been a total of 38 cases of sexual assault and two reported rapes at the We Are Sthlm festival in 2014 and 2015.

It followed a report in the Dagens Nyheter (DN) newspaper based on a memo issued to police ahead of the 2015 festival that groups of men and boys were targeting "young girls" at the festival.

According to the memo about 50 youths, mainly Afghan refugees, were believed to be behind the attacks and several were arrested but none charged.

Prime Minister Kjell Stefan Löfvén called for an investigation into why no-one was charged in connection with the attacks following the report, but police said they had charged a 15-year-old boy from west Stockholm in connection with the alleged assault and sexual assault of two 14-year-old girls at the festival.

The festival's title is derived from a Stockholm postcode and is held annually for 12 to 19 year-olds in locations across the Swedish capital, including the Kungsträdgården Park close to the royal palaces.

Police reported "relatively few" arrests in the wake of last year's festival through a notice posted on their website, however documents sent to AFP news agency and DN show that there were 17 allegations of sexual assault and one of rape at the 2014 festival, while the following year there were 19 sexual assault allegations and one of rape.

Police said they would fully investigate the crimes, and establish why the public were not made aware of them at the time. Peter Agren, who was in charge of the 2014 policing operation, said that police wanted to avoid inflaming anti-immigrant feelings and playing into the hands of far-right Swedish Democrats.

In Germany, police have been accused of covering up mass sexual assaults allegedly committed by asylum seekers against women and girls outside Cologne's main train station on New Year's Eve.