Frontex, the EU's border agency, said contingency plans are underway for any big shifts in migrant movements, with the organization's deputy executive director, Berndt Korne, naming Albania, the western Greek coast and Montenegro as possibilities.
The minister said that Turkey aims to build high-standard temporary shelters to house economic migrants who are returned to Turkey but do not qualify for refugee status in the country.
In exchange for taking back migrants, Turkey - already hosting about 2.7 million Syrian refugees on its soil - is driving a hard bargain, and it surprised its European counterparts at the start of the talks on Monday with further demands.
He also said that candidate country Turkey will meet its obligations to win visa-free travel to the European Union by May 1.
Ankara's European Union affairs minister Volkan Bozkir also underlined Thursday that the deal would not be retroactive, and would "not include the existing refugees on the Greek islands".
Greece's refugee crisis has sharply worsened in recent weeks after Austria and several Balkan countries began imposing border restrictions and closures.
German Chancellor Angela Merkel has renewed her criticism of moves by other European countries to shut borders to migrants, which she said will not create a sustainable solution.
Their reactions flew in the face of the response of EU President Donald Tusk, who welcomed the Balkan route closure as being part of a collective response from the bloc. Croatia, Serbia and Macedonia immediately followed the lead.
"Not a question of unilateral actions but common EU28 decision..."
Austria's interior minister says the Balkan migrant route should remain closed permanently and that the "clock will not be turned back".
Klaas Dijkhoff, the Dutch minister who chaired the meeting, said the mix of expulsion and legal resettlement should deter smuggling and help Turkey: "We have to show that it doesn't pay to use a trafficker and come to Europe in an illegal way and we have to show Turkey we are not leaving them with all the work".
Echoing Merkel's position from the past that a "privileged partnership" would be better, Weber said: "if Turkey wants a partnership with us then it's important to make sure that Turkey doesn't turn away from Europe". Thousands of migrants are stranded in Greece.
Muddy conditions after three days of rain at a refugee camp on the Greek-Macedonian border have left many struggling to re-pitch their small camping tents in the deteriorating conditions.
He said last week "we experienced the swift relocation of 287 people", the vast majority from Greece.
"This will be a major win for smuggling groups", said Tuesday Reitano of the Global Initiative against Transnational Organized Crime, referring to the EU-Turkey deal.