Dimitris Avramopoulos said EU states should be prepared to crack down on those with no legal right to be in the union – before they go off the radar.
The European Union Migration Commissioner said: “Return rates have to be improved. Member states should also use the possibility to place migrants in detention if there is a risk of absconding and for a sufficient period to be able to complete the return and readmission procedure.”
He said migrants awaiting deportation should be kept in comfortable, clean facilities – with no “concentration camp” implications.
Mr Avramopoulos said: “The ones who are not entitled to refugee status, they have to be returned. But in meantime they have to stay somewhere, in very dignified condition, in order to avoid absconding.
“It should never be considered something like a concentration camp.”
Brussels estimates there may be around one million people in the EU who should be sent back but that only about a third of those awaiting return are actually being sent back.
While EU law sets out the minimum common standards for returns, some member states had stricter domestic rules that could be eased to streamline the process, the Commission said.
It recommended shorter appeals deadlines, issuing return decision with no expiry date and considering more detentions, including for minors, which is barred now by some member states.
It said EU states should be less coy about detaining people for the maximum allowed pre-deportation time-limit of 18 months if that was needed to ensure an effective deportation.
Mr Avromopoulous concluded by demanding more to be done to help process legitimate migrants.
He said states needed to accept more migrants arriving across the Mediterranean in Italy and Greece or face penalties.
He said: “If the member states do not increase their migrant quota soon, the Commission will not hesitate to use its powers conferred by treaties against those who will not comply with its obligations.
“The current rate remains well below expectations and below the target agreed by the European Council of at least 3,000 monthly transfers from Greece and at least 1,500 from Italy.”