A Turkish coast guard ship patrols in the Aegean Sea, off the Turkish coast, April 20, 2016. REUTERS/John MacDougall/Pool

ATHENS (Reuters) - Turkish demands are posing obstacles to a NATO mission in the Aegean sea aimed at countering criminal networks smuggling migrants and refugees into Europe, Greek Prime Minister Alexis Tsipras said on Friday.

Speaking after a meeting with NATO Secretary-General Jens Stoltenberg in Athens, Tsipras said obstacles included not having full operational access in the region.

“Greece will undertake every effort so that NATO’s mission contributes to the solution of the crisis,” Tsipras said.

“Unfortunately it’s clear that the obstacles .. arise from Turkey’s unilateral demands and positions. Demands and positions which unfortunately are also expressed through a rise in activities which violate our airspace.”

NATO sent its ships into Greek and Turkish waters in the Aegean in March. On Thursday, it said the number of migrants and refugees crossing the sea from Turkey was falling significantly but smugglers can rapidly change routes and authorities must not reduce security efforts prematurely.