Updated

Greece's prime minister says relations between his country and Turkey are experiencing a "period of instability," and is stressing that Greece will not negotiate about any part of its territory amid increased tension with its eastern neighbor.

Speaking from the small eastern Aegean island of Kastelorizo, which he visited to inaugurate a desalination plant, Prime Minister Alexis Tsipras said Tuesday that he had a "message of cooperation" for Greece's eastern neighbor, but also "a message of determination."

Greece and Turkey have seen deteriorating relations in recent weeks over disputed Aegean boundaries and oil-and-gas drilling rights off the divided island of Cyprus. On Monday, Ankara accused Athens of provocation after a Greek flag was hoisted on an uninhabited islet in the eastern Aegean.