Turkey said Wednesday it would extend a gas exploration mission in the eastern Mediterranean that has raised hackles in neighbouring Greece, defying warnings from Western countries.

The Oruc Reis research vessel had been scheduled to end its work Thursday, but will now remain at sea until October 27, the Turkish navy said in a NAVTEX maritime announcement.

Oruc Reis has become the symbol of Ankara's appetite for natural gas in the eastern Mediterranean, where discoveries of significant reserves in recent years has triggered a rush for the so-called "blue gold".

Prospective fortunes to be made have reignited long-smouldering disputes over maritime borders between Turkey and Greece.

Athens says Ankara is breaking international law by prospecting in Greek waters, including near the island of Kastellorizo.

Turkey insists that it is within its rights in the energy-rich Mediterranean region, saying that the tiny island of Kastellorizo shouldn't count for imposing Greek sovereignty.

Oruc Reis' initial deployment in August sparked a weeks-long diplomatic crisis until the ship returned to port last month.

But last week it was sent out again, extinguishing hopes the tensions could be eased.

Greek Prime Minister Kyriakos Mitsotakis on Wednesday accused Turkey of playing out "imperialist fantasies" in the neighbourhood, while his government has asked the EU to look into suspending its customs union with Turkey.