MYTELINI, Greece — Before a long-negotiated European Union accord with Turkey went into effect last month, the breezy Greek island of Lesbos, set in the shadow of the Turkish mainland, was a port of passage for hundreds of thousands refugees seeking to travel further into Europe.
On Monday, the Greek and European Union authorities effectively started ushering people out, as a phalanx of police officers began enforcing a program of mass deportations of migrants back to Turkey.
As the sun rose over the Aegean Sea, the final leg of many refugees' journey to reach European shores, more than 100 officers from the European border agency Frontex marched 136 migrants who had been held in a closed, military-run camp here onto the ramp of two ferries.
With Greek riot police flanking the port, the boats set sail to the western Turkish town of Dikili, where the migrants — mostly Pakistanis — disembarked and were taken into tents for processing before being loaded onto buses. Turkish officials blocked journalists' access to the migrants and declined to comment on where they were being taken.
No Syrian refugees were present in the first group of migrants that arrived back in Turkey Monday, Volkan Bozkir, the European affairs minister for Turkey, said in a statement Monday.
Turkish officials have said that non-Syrians would be deported under the new deal, but it was not immediately known whether the migrants being returned to Turkey Monday would face deportation.
Turkish officials have indicated, however, that people believed to be economic migrants will at some point be sent back to their home countries.
Around 66 migrants were also shipped back to Turkey Monday morning from the Greek island of Chios, where riots recently broke out among asylum seekers who feared that they might not be able to stay in Europe.
More than 800 migrants broke out of a military camp there Saturday to protest what humanitarian groups said were prisonlike conditions.
Separately, Germany announced it was preparing to receive 40 Syrians, mostly women and children, from Turkey later Monday, as part of a broader EU initiative intended to help process asylum seekers and to deter illegal crossings into Europe from Turkey — as well as the smugglers behind them.
Turkey and the European Union sealed a deal last month requiring migrants who illegally reach Greece from Turkey after March 20 to be returned to Turkey unless they qualify for asylum — a status that was recently limited to Iraqis and Syrians.
In return, the European Union has pledged to take in thousands of Syrian refugees from Turkey as well as to give Ankara more than 6 billion euros (about $6.8 billion) in aid to improve conditions for migrants living in Turkey.
The agreement also calls for visa-free travel for Turkish citizens traveling in the Schengen area of the European Union, which covers most of the Continent, if Turkey meets certain conditions by the summer.
Whether the deal works is something all of Europe is waiting to find out. In particular, it is unclear whether the deportations, which are likely to be small at the outset, can be scaled up sharply. Greece is still waiting for thousands of police officers and specialists on asylum from other EU countries to arrive to help with the process.
It is also unclear whether the more than 50,000 migrants stuck on the Greek mainland will wait calmly, or whether tensions will flare up again, especially in squalid makeshift camps in Piraeus, the port of Athens; in Idomeni, on Greece's northern border; and in military camps on the Greek islands.
Riots have broken out in the past week in several places around Greece among migrants, many of whom have little idea of how the asylum process works and have grown increasingly fearful that, having made it this far, they may be deported back to Turkey or their homeland.
"The main objective is to stick a blow to the business model of human trafficking from the Turkish coasts to the Greek islands," said Giorgos Kyritsis, the Greek government's spokesman on migration.
"The deal aims to convince people that until now were victims of the smugglers, that it is against their interests to risk their lives and pay all this money in order to make it to the Greek islands ," he said, "and that the shortest and the only legal way to get to Europe is to be included in the resettlement program underway in Turkey."
Even as the Turkish officials carried out a series of raids to crack down on smugglers in recent days, dozens of migrants, undeterred by the new regulations, left for Greece in rubber dinghies Monday and were intercepted by the Greek and Turkish coast guards.
The migrants returned to Turkey Monday were not failed asylum seekers, but people who had not applied for asylum. The processing of asylum applications on the Greek islands is expected to start Thursday. No one who has applied for asylum will be sent back before receiving a definite answer from the authorities, Kyritsis said.