Police said on Wednesday they had broken up an international criminal organization smuggling migrants and refugees through Greece, one of the main gateways into the European Union.
Officers arrested 12 people from Pakistan, Egypt, Iraq and Syria in raids on apartments and other locations across Athens early on Sunday and confiscated hundreds of fake identity cards, passports and other documents, the force said.
The smugglers were divided into six units which helped migrants travel from Turkey via the Greek island of Kos on to Macedonia and Italy on planes, buses and trains, the statement said.
Police attached an organization chart of at least 30 suspects, plus an unknown number of associates in Turkey, drawn up after what they called one of their biggest operations against people smugglers.
The gang gave fake asylum registration documents to migrants arriving on Kos in exchange for about 3,000 euros ($3,400) each, the police added.
Hundreds of thousands of migrants and refugees - mostly from war-torn Syria, Afghanistan and Iraq - have crossed the Aegean Sea this year from Turkey, attempting a short but risky trip in wooden boats or rubber dinghies. Many have died at sea.
The surge in people fleeing violence and poverty in Africa and the Middle East has increased pressure on Greece which is struggling to overcome its worst economic crisis in decades.
Almost 400,000 migrants have arrived in Greece this year, the U.N. refugee agency UNHCR said on Friday.
Prime Minister Alexis Tsipras has made managing migration a top priority for his re-elected government and visited the island of Lesbos with Austrian Chancellor Werner Faymann on Tuesday to inspect reception centers and discuss cooperation.