ATHENS, Greece — Greece detained hundreds of refugees and migrants on its islands Monday, as officials in Athens and the European Union conceded a much-heralded agreement to send thousands of asylum-seekers back to Turkey is facing delays.
Migrants who arrived after the deal took effect Sunday were being led to previously open refugee camps on the islands of Lesbos and Chios and held in detention, authorities on the islands said.
EU countries are trying to avoid a repeat of the mass migration in 2015, when more than a million people entered the bloc. Most were fleeing civil war in Syria and other conflicts, traveling first to Turkey and then to the nearby Greek islands in dinghies and small boats. Efforts to limit migration have run into multiple legal and practical obstacles.
Under the deal, Greek authorities will detain and return newly arrived refugees to Turkey. The EU will settle more refugees directly from Turkey and speed up financial aid to Ankara. The two sides, however, are still working out how migrants will be sent back.
"We are conscious of the difficulties," EU Commission spokesman Margaritis Schinas said in Brussels.
"And we are working 24-7 to make sure that everything that needs to be in place for this agreement to be implemented soon is happening."
Commission officials said support staff needed to implement the deal — including hundreds of translators and migration officers — would not start arriving until next week. Returns, they said, cannot start until Greece changes its law to recognize Turkey as a "safe country" for asylum applications.
The human rights group Amnesty International sharply criticized the plan.
"Turkey does not offer adequate protection to anyone," Iverna McGowan, the head of Amnesty's EU office, told The Associated Press, accusing Turkey of routinely forcing Syrians back across the border.
Migrants, meanwhile, continued to reach Greek islands in large numbers, as smugglers appeared to be opting for more overnight crossings and increasingly dangerous routes.
Four people died Sunday while trying to reach Greece, two men off the island of Lesbos and two girls off the tiny islet of Ro, the coast guard said. More than 1,600 people made the crossing to Greece on Sunday, and 262 were rescued in five incidents after vessels sank or were in distress.
"We face an uphill effort. Implementation of this agreement will not be an easy issue," Greek Prime Minister Alexis Tsipras said.
He met in Athens with EU Migration Commissioner Dimitris Avramopoulos and urged him to increase pressure on Turkey to crack down on smugglers.
Migrants and refugees have been stranded in Greece since Austria and Balkan countries started border closures in recent weeks. The number stranded reached 50,000 on Monday, with some 12,000 still camped out on Greece's closed border with Macedonia.
On the Greek mainland, army personnel expanded refugee shelters at sites in the central and northern parts of the country — mostly at former army bases — so migrants who traveled to the Greek islands before the agreement came into effect could be resettled.
"We are creating between 500 and 1,000 additional shelter places every day ... and the total right now is 36,000," Migration Minister Ioannis Mouzalas said.
On Monday, monitors from Turkey's interior Ministry arrived on Lesbos, Chios and three other Greek islands to help supervise the agreement and were to stay for at least one week.
Cook reported from Brussels. Raf Cassert in Brussels, Suzan Fraser in Ankara, Turkey, and Costas Kantouris in Thessaloniki, Greece, contributed to this report.
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