Greece began returning migrants from the island of Lesbos to Turkey on Monday under a landmark European Union deal aimed at stopping the uncontrollable influx of migrants and refugees into Europe since last year.

Under the EU-Turkey deal, Ankara will take back all migrants and refugees, including Syrians, who enter Greece illegally in return for the EU taking in thousands of Syrian refugees directly from Turkey and rewarding it with more money, early visa-free travel and progress in its EU membership negotiations.

Two Turkish-flagged passenger boats carrying 131 migrants set sail from Lesbos to the Turkish town of Dikili as the sun rose over the Aegean Sea early on Monday, a Reuters witness said.

Most returnees were from Pakistan and Bangladesh, according to Ewa Moncure, a spokeswoman for EU border agency Frontex. Each migrant was accompanied by a plainclothes Frontex officer. Greek riot police squads also boarded the boats.