Buses carrying hundreds of migrants for deportation to Turkey have arrived at the Greek island ports of Lesbos and Chios.

Two Turkish leisure vessels are waiting to pick them up. The migrants will be escorted by officers from the EU border agency Frontex. On Lesbos, crews were earlier seen loading supplies onto the ships -- a small ferry and a catamaran.

These developments are happening because of a controversial deal between the EU and Turkey last month. The deal is designed to halt new arrivals along the most popular route through Turkey, while all "irregular migrants" arriving after March 20 face being sent back. Each case is meant to be examined individually.

For every Syrian refugee returned, another will be resettled from Turkey in the EU, with numbers being capped at 72,000. The deal has been criticised by rights groups on ethical grounds.