The agreement between the EU and Turkey to tackle the migrant crisis has formally come into effect.
Under the deal, migrants arriving in Greece are now expected to be sent back to Turkey if they do not apply for asylum or their claim is rejected.
The influx of people crossing to Greek islands grew ahead of the deadline, and Greece said immediate implementation of the deal would not be possible.
Meanwhile, thousands rallied against the deal in several European cities.
The deal says that for every Syrian migrant sent back to Turkey, one Syrian already in Turkey will be resettled in the EU.
However, there were still many doubts about the implementation of the agreement, including how the migrants would be sent back.
Some 2,300 experts, including security and migration officials and translators, are set to arrive in Greece to help enforce the deal.
But Greek officials said none of the experts had yet arrived and the deal could not be implemented immediately as key details still needed to be worked out.
“A plan like this cannot be put in place in only 24 hours,” said government migration spokesman Giorgos Kyritsis, quoted by AFP.
