SARAJEVO (Reuters) - Bosnian and Croatian police said on Thursday they had arrested 13 people suspected of smuggling at least 100 migrants from Turkey into the European Union.

Four Bosnians, two Turkish citizens with Bosnian residence and seven Croatians are thought to have been part of an international criminal ring which charged migrants 3,000 to 5,000 euros ($3,235 to $5,395) to get them from Turkey to the European Union.

The so-called Balkan route for migrants trying to reach western Europe via Turkey, Greece and countries of the former Yugoslavia was shut down last year when Turkey agreed to stop the flow in return for EU aid and a promise of visa-free travel for its own citizens.

But Adnan Kosovac, a Bosnian border police official, said the suspects had been taking advantage of visa-free travel between Turkey and Bosnia to legally transfer migrants by land or plane to Bosnia and then smuggle them to EU member Croatia.

Police said the 13 arrests were made under an operation codenamed Bosphorus, launched eight months ago and coordinated with law enforcement in Turkey, Bulgaria, Romania, Hungary, Albania, Serbia and Montenegro. They said a further 60 arrests had been made over that period.