"This is a historic day," Turkish prime minister Ahmet Davutoglu said after a EU deal with Turkey aimed at easing the migration crisis.
Under the terms of the agreement, Greece is to start returning migrants arriving by boat from Turkey from Sunday.
The agreement involves closing the EU border on March 20 and sending back migrants who arrive in Greece after that date to Turkey.
Cameron asks EU leaders to back deployment of more international patrol ships close to Libyan coast in bid to deter migrant smugglers.
David Cameron will tell his European colleagues that the migration route from Libya to southern Italy is about to begin once more.