The agreement between the EU and Turkey on stemming the flow of irregular migrants officially entered into force on Sunday.

The deal, which had been agreed in principle earlier in March, was finally approved at a meeting between EU leaders and Turkish Prime Minister Ahmet Davutoglu on Friday.

The deal foresees the return of all illegal migrants from Greece to Turkey if they do not apply for asylum or if their application is rejected.

According to the agreement, for every Syrian refugee returned to Turkey, a Syrian already in Turkey will be resettled in the EU.

However there are uncertainties over the implementation of the deal as it remains unclear how migrants will be sent back.

Around 2300 experts, including security and migration officials, are expected to arrive in Greece to aid the implementation of the agreement, the BBC informs.

Greek officials informed that none of the experts had yet arrived and the deal could not be implemented immediately as there were still key details to be clarified.

The agreement is aimed at discouraging people from attempting the deadly crossing of the Aegean Sea between Turkey and the Greek islands.

In return for accepting the deal, Turkey will receive an aid of EUR 3 B to deal with the migrants, with further EUR 3 B to be allocated once the initial resources are used.

The EU also promised to grant Turkish citizens with visa-free travel to countries from the Schengen Area by the end of June and to re-energise negotiations for Turkey's accession to the EU.