The operation is set to begin tomorrow on the Greek island of Lesbos, which has served as a gateway for hundreds of thousands of refugees and migrants arriving in Europe from Turkey in the past year.
Details of how the operation will proceed are sketchy, with Greek officials tight-lipped today over who and how many migrants will be sent back across the Aegean Sea.
Turkish Interior Minister Efkan Ala said his country had made preparations to receive 500 people tomorrow, and that the Greeks had given the names of 400.
The European Union signed the controversial deal with Turkey in March as it wrestles with the continent's worst migration crisis since World War II, with more than a million people arriving from the Middle East and elsewhere last year.
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Under the agreement, designed to discourage people from making the risky Aegean crossing, all "irregular migrants" arriving since March 20 face being sent back, although the deal calls for each case to be examined individually.
The deal has faced heavy criticism from human rights groups, who have questioned whether it is legal and ethical.
"We don't know what is going to actually happen," senior UN migration official Peter Sutherland said yesterday. "But if there is any question of collective deportations without individuals being given the right to claim asylum, that is illegal."
Yiorgos Kyritsis, spokesman for Greece's refugee coordination unit, insisted Monday's operation "involves people who have not requested asylum.