It concerns at least twelve occasions when it is suspected that people have been smuggled near the town of Didymóteicho in northeastern Greece, close to the border with Turkey.
“An investigation has so far shown that the police have been in contact with networks operating in a neighboring country at least since October,” the police write in a statement.
The investigation contains evidence, including nearly 60 mobile phones and money from Turkey and several other countries.
Thousands of migrants, mainly from Syria, Afghanistan and Pakistan, have entered Greece from Turkey in recent years in the hope of moving on to other European countries.