Greek Prime Minister Alexis Tsipras criticized neighboring Turkey Friday for preventing a NATO force in the Aegean Sea from expanding its activities further south along the two countries' borders as a part of its deployment to help tackle the refugee crisis.

NATO has deployed ships in the northern Aegean to help combat smugglers taking people from Turkey to Greek islands, but it has not deployed in the southern Aegean area. Greece says this is because Turkey objects, considering it to be a demilitarized area.

"Unfortunately ... I consider that we still have a significant way to go regarding NATO's activity and the effectiveness of this activity in the Aegean," Tsipras said, speaking after meeting in Athens with NATO Secretary-General Jens Stoltenberg. "Mainly regarding the access and development of the NATO force's capabilities in the entirety of the operational area."

Greece and Turkey have long been at odds over a number of issues, including territorial ones in the Aegean, and Athens frequently complains of Turkish fighter jets violating its airspace.

"It is clear that the obstacles to which I am referring arise from the unilateral claims and positions of Turkey. Claims and positions which, unfortunately, are expressed with an increase" in airspace violations, the Greek prime minister said.

"It is clear that Greece will not accept or tolerate any actions which violate or dispute our sovereign rights."