The incidents included abuse by known sex offenders visiting the reception centres as well as residents of the centres, Due said, adding that police were reviewing every alleged case.

“We are looking very seriously at every individual case, and based on our information it’s very likely that children living in reception centres in Norway have been and are being subjected to sexual abuse,” he said. “But generally there is low criminal activity in and around the reception centres.”

Due said that police wouldn’t provide details about the alleged cases at this stage.

Last year, more than 31,000 people applied for asylum in Norway of whom 5,300 were unaccompanied minors.

In neighbouring Sweden, police said they have arrested 14 men on suspicion of preparing attacks on an asylum-seekers’ center near the capital, Stockholm.

Various weapons, but no firearms, were found in cars during the arrests on Monday evening in Nynashamn, 60km south of Stockholm, police spokesman Lars Bystrom said. He didn’t identify the men, but Swedish Radio cited local police officer Lars Alvarsjo as saying they were Polish, and possibly members of right-wing groups.

The arrests come amid increasing opposition to migrants and reports of attacks against refugee centers in the Scandinavian country, which has been a top European destination with 163,000 arrivals last year. Previously known for its generous immigration policies welcoming refugees fleeing war and persecution, the Social Democratic led-government reversed course late last year tightening border controls and immigration regulations.

Meanwhile, The International Organisation for Migration announced that 409 people have died this year trying to cross the Mediterranean Sea, and migrant crossings in the first six weeks of 2016 are running at nearly 10 times the rate of the same period last year.

IOM says 76,000 people have reached Europe by sea, nearly 2,000 per day, since January 1.