[Greek PM Tsipras meets NATO Secretary General Stoltenberg at the Maximos Mansion in Athens]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.