A Greek fighter pilot died on Thursday when his plane crashed in the Aegean while returning from a mission to intercept Turkish jets, officials said.
"A Greek pilot (has entered) the pantheon of heroes," Defence Minister Panos Kammenos said in a tweet.
"He fell... fighting to defend national sovereignty and territorial integrity," he said.
Greek Prime Minister Alexis Tsipras said the pilot, a father-of-two named as Georgios Baltadoros, died "in the line of duty."
The Greek armed forces will observe a three-day period of mourning over the accident, the defence ministry said.
The Greek airforce said Baltadoros was fatally hurt when his Mirage 2000-5 fell into the sea while preparing to land "after concluding an operational mission."
Reports said the pilot may have blacked out during a combat exercise on the return home.
A Greek general staff source told AFP that the plane was returning from a mission to intercept Turkish fighter jets.
"The mission was over and the plane was returning," the source said.
"We still don't know if there was an actual engagement with the Turkish airforce," the officer added.
Citing military sources, state TV ERT said there had been no engagement with the Turkish airforce.
In Turkey, state-run Anadolu agency quoted Turkish security sources as saying there were no Turkish air force jets in the area at the time of the incident.
ERT said the warplane fell in the sea shortly before it was due to land at an airfield on Skyros island in the central Aegean.
Greek fighter planes are regularly scrambled to intercept Turkish jets entering what Athens considers Greek airspace over the Aegean, occasionally engaging in mock dogfights.
The accident comes at a period of heightened tension between regional rivals and NATO allies Greece and Turkey.
Earlier this week, Greek soldiers fired warning shots at a Turkish helicopter after it approached the small island of Ro, which is on Greece's border in the southeastern Aegean Sea.
Turkish President Recep Tayyip Erdogan and members of his government have escalated verbal attacks on Greece after its failure to extradite eight Turkish soldiers that Ankara said were part of an attempted 2016 coup.
In March, Turkey captured and is still holding two Greek soldiers who crossed the border, allegedly whilst getting lost in the fog on patrol.
In 2006, a Greek pilot was killed when his plane collided with a Turkish jet during a mock dogfight in the Aegean.
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