Turkish president Recep Tayyip Erdogan claimed on Tuesday that the Greek military has been using its installations on islands in the Aegean Sea to harass Turkish military aircraft flying in international airspace, warning that Ankara would not accept continued provocations and would retaliate in the future.

Erdogan’s announcement came during a joint press conference in Sarajevo, the capital of Bosnia and Herzegovina, with that country’s collective head of state. The Turkish leader claimed in his remarks that Greek operators of the S-300 missile system had locked onto Turkish jets operating in international waters, implicitly threatening to shoot the planes down, although no missiles were fired. The Greek military has denied that the incident took place.

“If such illegitimate threats against us continue from there, [our] patience will end,” Erdogan said, claiming that, “when the time comes, [we might] come suddenly one night.”

“When the time comes, necessary actions will be taken,” he added, although he did not specify how Ankara sought to retaliate.

Although Greece and Turkey are historical rivals, both are members of NATO and have not formally been at war since 1922. Despite their broader geopolitical alignment, however, both Athens and Ankara have maintained an ongoing regional dispute regarding the ownership of the Aegean Sea. In recent years, Greece, which owns nearly all of the Aegean islands, has claimed that its airspace extends up to ten nautical miles from the shore of any island within the sea. Because all of the islands are within six miles of each other, this interpretation would give Greece control over the entire Aegean—an interpretation that Turkey has rejected.

Prior to Erdogan’s remarks in Sarajevo, the Turkish Foreign Ministry sent a letter to twenty-five members of the European Union, the five permanent members of the United Nations, UN Secretary-General Antonio Guterres, EU High Representative for Foreign Affairs Josep Borrell, and NATO Secretary General Jens Stoltenberg. In the letter, Turkish officials broadly outlined the Turkish position on the dispute and urged international cooperation to de-escalate the crisis, while emphasizing that Greece’s actions had been “unlawful” and had violated the previously agreed non-military status of the Eastern Aegean.

Greek officials have denied wrongdoing, and the Greek Foreign Ministry condemned what it characterized as the “outrageous daily slide” of threats from Erdogan and other Turkish officials.

Trevor Filseth is a current and foreign affairs writer for the National Interest.

Image: Reuters.