Police in Greece and the Czech Republic have arrested more than 20 people suspected of forging travel documents for migrants trying to enter Europe.
European police agency Europol said visas and passports were sold for up to £2,500 ($3,600) and sent across the EU, Africa, the Middle East and Asia.
Greek police said the criminal networks were also involved in smuggling people across borders.
About 100 people are still wanted in Greece and other countries.
Europol said the network was based in Athens and consisted of two criminal groups, one run by Sudanese people and another by Bangladeshis, and 16 people have been arrested in Greece.
Both groups forged passports, national ID cards, Schengen visas, driving licences, asylum seekers' registration cards and residence permits, police said.
Ten suspects were arrested in the Czech Republic, where a separate group would send stolen or lost travel documents to Athens for the Bangladeshi and Sudanese groups to falsify.
A police spokesman in the Czech Republic said seven migrants were also arrested for using forged documents.
The Sudanese-led group helped up to 15 migrants a month enter the EU at a cost of up to nearly £4,000 ($5,800, €5,200) per head, Greek police said.
In other developments in the migrant crisis across Europe on Tuesday:
- The death toll from migrant shipwrecks in the Mediterranean last week has been revised upwards to 1,000. International Organization for Migration spokesman Flavio Di Giacomo gave the new figure which comes after an estimate on Sunday of 700 deaths by the UN refugee agency.
- A camp for migrants is to be set up in the north of Paris within the next six weeks, after hundreds of migrants have been camping rough in the French city.
- A fireman in Germany has admitted setting fire to a house where seven Syrian refugees were living. He said he did it because he was frightened of the refugees, who people said were criminals. He said he later realised they were "awfully nice". He and an accomplice are facing seven charges of attempted murder in a trial that is expected to last 11 days.