NATO Secretary-General Jens Stoltenberg says efforts to stem the tide of migrants seeking the shores of Europe are working.

Speaking in Ankara, he said the collective effort is "making a difference" and that the number of migrants crossing the Aegean Sea is "significantly down."

Under an EU-Turkey deal signed last month, migrants arriving on Greek islands from the Turkish coast from March 20 onwards face deportation to Turkey unless they successfully apply for asylum in Greece.

The International Organization for Migration says Greece has seen fewer than 70 arrivals per day in the past 10 days, down from nearly 1,500 of arrivals per day before the deal was struck.

NATO began patrolling the Aegean Sea in February to help stop the smuggling of migrants.