Turkey will redeploy the research ship at the centre of an energy row with Greece to the eastern Mediterranean on Monday, a decision slammed by Athens as a "direct threat to peace".
The row over gas exploration in the eastern Mediterranean saw the two NATO countries stage rival military drills in August in strategic waters between Cyprus and the Greek island of Crete.
Greece claims rights over the waters around its island of Kastellorizo but Turkey says the island's close proximity to its longer coastline makes the territory a legitimate area for its vessels to explore.
The Turkish navy said the Oruc Reis ship will carry out activities in the region, including the south of Kastellorizo, until October 22 in a message sent to the maritime alert system NAVTEX late on Sunday.
The vessel will be joined in the latest "seismic survey" mission by two other ships called Ataman and Cengiz Han, the message said.
Turkish Energy Minister Fatih Donmez delivered a defiant message via Twitter on Monday that Turkey "will continue to search, dig and protect our rights".
"If there is (natural gas), we will absolutely find it," he said.
But Greece's foreign ministry on Monday lambasted the move as a "direct threat to regional peace and security" and accused Turkey of being unreliable.
The ministry added Ankara did not "sincerely desire dialogue".
In turn, the Turkish foreign ministry slammed its Greek counterpart's statement, criticising Athens's "maximalist" demands.
"It's not acceptable for there to be a challenge to the activities 15 kilometres (9.3 miles) away from the mainland of our country which has the longest coastline in the eastern Mediterranean," it said in a statement.
Ankara first deployed the Oruc Reis and warships to disputed waters on August 10 and extended the mission, ignoring repeated calls to stop by Greece and the European Union.
- 'Committed to diplomacy' -
Turkish Defence Minister Hulusi Akar also hit out at Greece, stressing that Ankara's actions in the Aegean and Mediterranean were "not a threat to anyone".
"They are doing everything they can to increase tensions," Akar told reporters in Ankara.
The Oruc Reis was pulled back to shore last month in what many hoped was a sign the two sides could resolve the issue through dialogue.
Turkish President Recep Tayyip Erdogan said at the time that the withdrawal was designed to give diplomacy a chance.
But Turkish officials also insisted the ship was in port for planned maintenance and would return to the eastern Mediterranean to continue its work.
In his tweet on Monday, Donmez said maintenance work was finished and the ship could now restart its scan of the Mediterranean.
Erdogan's top press aide Fahrettin Altun said Turkey was still "committed to a diplomatic solution and encourages all parties, including Greece, to support Turkey's diplomatic initiatives."
But Altun tweeted in English "there can be no negotiations if you say 'what's mine is mine and what's yours is negotiable'."
- Sanctions threat -
The announcement dashed hopes raised when Turkey and Greece agreed to exploratory talks last month following diplomatic efforts led by Germany to defuse the crisis.
The talks had been stalled since 2016 and the expectation was for their resumption in Istanbul but no exact date was given.
The Turkish and Greek foreign ministers also met last week on the sidelines of a security forum in Slovakia's capital Bratislava in the highest-level talks since tensions began.
The ministers agreed that a date should be set for the start of talks, according to a Greek foreign ministry source.
At a summit earlier this month, the European Union threatened sanctions if Turkey failed to stop what the bloc says is illegal drilling and energy exploration activities in waters claimed by Cyprus and Greece.
The German foreign minister is expected to visit Ankara on Wednesday, according to Turkish state broadcaster TRT, where the eastern Mediterranean will be high on the agenda.