Police in Greece on Tuesday said they had arrested three members of a Greek NGO on suspicion of helping migrants illegally enter the country.
The members of Emergency Response Centre International (ERCI) were detained on Lesbos, the Greek island with the most arrivals.
"The activities of an organised criminal network that systematically facilitated the illegal entry of foreigners were fully exposed," a police statement said.
Members of the group were in contact with migrants and refugees on social media groups and "actively assisted" their illegal entry into Greece from 2015 onwards, according to the statement.
To keep tabs on migrant flows, the accused also illegally monitored Greek coastguard and EU border agency Frontex radio traffic.
And any information gathered was not shared with Greek authorities, the police said.
Overall, six Greeks and 24 foreign nationals were implicated in the case, they added.
ERCI did not immediately respond to a request for comment.
Lesbos has been a key gateway into the European Union since the start of the bloc's migration crisis in 2015.
At the height of the influx, some 5,000 refugees and migrants, mostly from war-torn Syria, were landing on the island's beaches on a daily basis.
The police on Tuesday also said that two members of the group had been arrested in February on board a jeep with concealed fake army license plates.
© 2018 AFP