A wave of sex crimes made headlines in Oulu late last year, with all of the suspected perpetrators being foreign-born men who had arrived in Finland either as quota refugees or asylum-seekers.

Police in Oulu, a city of approximately 200,000 people in Finland, have launched a probe into the suspected rape of two girls aged 16 and 18. The reported crime took place last weekend in a private home, according to Kaleva, a local newspaper.

Oulu police announced on Monday that one suspect had been arrested; he is said to have a foreign background and a residence permit. The case is being investigated as an aggravated rape; for the younger girl, the offence qualifies as aggravated sexual exploitation of a minor.

An Oulu law enforcement official was quoted as saying that there are other suspects, but she refused to go into further detail.

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Since late last year, Oulu police have been investigating multiple sexual assault cases involving underage girls and foreign men. All of the perpetrators are said to have come to Finland as asylum seekers and refugees, some from the Middle East. The number of the investigations has been rising since the police urged the public not to hesitate in reporting any further cases.

Last month, local authorities issued a temporarily ban on asylum-seekers and refugees visiting schools and childcare centres, after parents said they were worried about so-called integration visits due to the recent spate of sexual attacks.

According to a poll carried out by newspaper Helsingin Sanomat, roughly two-thirds of Finns said that "the different culture and religion of immigrants" were the most important reasons for the recent wave of sexual violence.

Finnish police state that people with a foreign background are responsible for a quarter of all reported sex crimes, despite constituting only 6.9 percent of the Finnish population.