The main airport in Ukraine's Crimea on Tuesday cancelled incoming flights from the capital Kiev but allowed several planes from Moscow to land, five days before a referendum called to join the Black Sea region to Russia.
A Ukrainian airline plane was turned back on its way from Kiev to Simferopol, the region's main city, and returned to the capital. Airport passenger information also showed an incoming flight from Istanbul, Turkey, had been cancelled.
But several flights came in from Moscow.
Armed pro-Russia groups have taken over control of the airport but until now had been allowing it to function normally for passenger traffic.
Tension has increased in the region before Sunday's referendum which pro-Russian leaders, backed by Russian forces, have called despite it being denounced as illegal by Ukraine's new rulers and Western governments.