Greek authorities on Monday began deporting refugees on boats headed to Turkey, as part of a controversial European Union plan to curb the tide of migrants entering Europe. Officials began escorting migrants at dawn onto ferries from the EU border-protection agency Frontex to ports on the Turkish coast. An estimated 4,000 migrants and refugees have been detained on Greek islands since the deal came into effect on March 20. The deportations began with migrants who did not apply for asylum or had applications that were declared inadmissible. In return for admitting migrants, Turkey was granted more financial aid and visa-free travel in the EU for its citizens.