ATHENS, Greece (AP) — Turkey is under growing pressure to consider a major escalation in migrant deportations from Greece, a top European Union official said Thursday, amid preparations for a highly anticipated summit of EU and Turkish leaders next week. European Council President Donald Tusk ended a six-nation tour of migration crisis countries in Turkey, where 850,000 migrants and refugees left last year for Greek islands. Tusk was careful to single out illegal economic migrants for possible deportation, not asylum-seekers. [...] he wasn't clear who would actually carry out the expulsions: Hungary has already called a referendum on EU plans for a mandatory quota system for settling migrants, and says it's was considering action to bolster its border fences with additional police and military personnel, and extending the fence to the Romanian frontier. Earlier Thursday, Tusk told officials in Athens that Europe had little chance of resolving the crisis without full respect of controls on the external borders of Europe's passport-free Schengen area — signaling pressure on Athens to do more to separate economic migrants from those fleeing war in Syria, Iraq and elsewhere.