Sweden has charged three men with organizing the smuggling of 170 migrants in minibuses from northern Italy across the EU's open-border zone to Scandinavia, prosecutors said on Friday.

Prosecutors said they believed the trio hired minibuses and drivers to transport the mostly Syrian migrants to Scandinavia from Milan train station in Italy in 2014.

"There they were simply walking around and asking if someone wants to go to Sweden or other parts of Scandinavia," presiding prosecutor Isabelle Bjursten told Reuters.

She said the suspects typically charged around 500 euros ($560) per person while often letting children travel for free, and earned around 150,000 Swedish crowns ($17,500), she said.

Police in Italy, Denmark, Germany and Austria stopped 15 of the mini-buses and camper vans in August and November 2014.

Of the three suspects, two have both Swedish and Iraqi citizenship while the third is a Syrian citizen, and they are between 35 and 37 years old, prosecutors said. If found guilty, they could get between six months and six years in prison. They were arrested in Sweden last year then freed pending trial.

After more than one million asylum-seeking migrants entered Europe in 2015, countries within the European Union's Schengen passport-free travel zone, including Sweden and Germany, reintroduced selective border controls to stem the influx.