Turkey issued a navigational warning, or Navtex, on Thursday evening announcing that its research vessel, Piri Reis, will conduct scientific surveys in the central Aegean, west of Chios and Lesvos, between October 4 and 14, according to the Kathimerini Greek media outlet.
This is the second time in less than a month that Ankara has announced plans to send the Piri Reis into contested waters, reigniting tensions over who has jurisdiction in parts of the Aegean where both Turkey and Greece claim continental shelf rights.
The Turkish Navtex covers a broad maritime zone extending from Thasos to Chios, encompassing the Aegean Sea, as well as Mykonos, Ikaria and the Fournoi islands. The announced research involves both Turkish territorial waters and international waters, but it also overlaps areas that Greece claims fall within its continental shelf and within the Navtex coordination zone administered by Athens.
Late on Thursday Greece issued its own counter-Navtex, valid until October 25, stressing that the Turkish notice illegally encompasses areas within the Greek continental shelf and Athens’ Navtex responsibility zone, as reported by Greek media.
Navtex, an international system used to communicate maritime safety information, often becomes a diplomatic flashpoint in the Aegean, where Ankara and Athens disagree on who has the right to issue such notices.
The announcement comes only days after the controversial cancellation of a planned meeting between Prime Minister Kyriakos Mitsotakis and President Recep Tayyip Erdoğan in New York.
A similar Navtex was issued in mid-September for the same vessel, although the Piri Reis ultimately did not carry out any research at that time. The ship remained anchored in İzmir marina throughout the announced survey period, which Greek officials interpreted as a possible sign of hesitation.
Athens responded to the September announcement with a large-scale military exercise across the Aegean on September 17, deploying more than 60 fighter jets, the entire Hellenic Navy fleet, special forces on 30 islands, and army units near the northern border with Turkey. The drill, which activated Delta Force, a joint formation of the Hellenic Armed Forces, was described by Greek officials as a demonstration of readiness to defend national sovereignty.
Turkey hit back on September 18 with another Navtex, repeating its long-held view that certain Greek islands must stay demilitarized under international treaties, citing the 1923 Lausanne and 1947 Paris peace treaties, which Ankara says prohibit militarization.
According to the September Navtex issued by Turkey’s İzmir station, the vessel’s track was set to take it west of Lesvos, south of Chios and onward to the islet of Kalogeros, located in open waters between Chios and Andros. Greece claims the planned route passes through sections of the Aegean that lie within the territorial waters of Greek islands and over areas it claims as its continental shelf.
The passage near Kalogeros carries additional symbolism, as Turkey has long objected to Greece’s inclusion of the islet almost year-round in a permanent firing range of the Greek Armed Forces.
Whether the Piri Reis will actually proceed with surveys this time remains to be seen, with Greek authorities expected to monitor the situation closely.
The Piri Reis is a Turkish-flagged research vessel operated by Dokuz Eylül University, based in İzmir, and used primarily for scientific and seismic research. It has been deployed for seismic surveys in the Aegean and Mediterranean since the 1970s. Its missions have repeatedly drawn protests from Greece when conducted in disputed zones.
Greece and Turkey, both NATO members, have a long history of disputes over maritime boundaries, airspace and territorial sovereignty in the Aegean. After years of tension over migration, energy rights and maritime borders, the two countries resumed high-level talks in December 2023, when President Erdoğan made his first visit to Athens since 2017 and signed a declaration of friendship. Prime Minister Mitsotakis reciprocated the visit in May 2024.