Turkey has extended until mid-September a controversial east Mediterranean gas exploration mission that has put it at odds with Greece and the rest of the EU.
Ankara deployed the Oruc Reis research vessel and warships to the disputed waters on August 10 and prolonged the mission twice.
Greece responded by staging naval exercises with several EU allies and the United Arab Emirates not far from smaller ones Turkey was conducting between Cyprus and Crete last week.
Turkey's most recent extension of the mission was until Tuesday, raising the possibility that a fast-escalating conflict in an energy-rich but volatile region that includes war-torn Libya and Egypt could cool off.
But in a message on NAVTEX, the international maritime navigational telex system, Turkey said late on Monday the seismic vessel's stay in the disputed waters would be extended until September 12.
The Turkish message said the Oruc Reis was being accompanied by Turkey's two other auxiliary vessels, the Cengiz Han and the Ataman.
Turkish President Recep Tayyip Erdogan vowed late Monday to continue the gas exploration work "with determination".
"God willing, we hope to get good news from the Mediterranean in a short span of time, too, as we got in the Black Sea," Mr Erdogan said.
Mr Erdogan was referring to Turkey's discovery of what officials said were 320-billion-cubic-metres of natural gas in the Black Sea, the biggest in Turkey's history.
Ankara's relations with Athens have deteriorated sharply, with strains over issues including migration and Turkey's decision to convert Byzantine-era churches into mosques.
Images published in the media last week showing Greek soldiers arriving on the island of Kastellorizo, known as Meis in Turkish, appear to have opened another front between the two uneasy Nato allies.
The island is only two kilometres from Turkey's famed seaside town of Kas in the Antalya province.
The Oruc Reis mission is being conducted near that island, with the navy also scheduling a series of live fire exercises further to the east this month.
Turkey accused Greece of trying to to "arm the island" despite a 1947 peace treaty that established its demilitarised status.
The Turkish foreign ministry lashed out at Greece's "provocative actions" at the weekend, while ruling party spokesman Omer Celik tweeted that Athens's attempt to arm the island amounted to a "new example of piracy".
But a Greek official said soldiers are already stationed on the island of Kastellorizo and the photos were from a "routine troop rotation."
Mr Erdogan fired back and said: "We will never succumb to piracy or banditry in the Mediterranean and the Aegean."
The European Union has repeatedly urged Turkey to stop the exploration activities and threatened to slap sanctions on Ankara if it refused to solve the dispute through talks.