A Turkish ship in the Eastern Mediterranean will extend its oil and gas exploration until August 27 in a move that will anger Greece, which has declared the survey to be illegal.
The Oruc Reis, which has been accompanied by Turkish warships, has been carrying out seismic surveys in water claimed by Cyprus and Greece.
It was expected to complete its work on August 23 but on Sunday the Turkish navy issued an advisory that said three vessels, including the Oruc Reis, would continue until August 27.
Seismic surveys are part of preparatory work for hydrocarbon exploration.
Turkey and Greece also disagree on flights over the Aegean Sea and the status of Cyprus, which is divided between the Greek Cypriot-controlled south and the breakaway Turkish Republic of Northern Cyprus.
There is widespread disagreement over resource claims on the continental shelves in waters dotted with mostly Greek islands.
The island of Kastellorizo, only 2 kilometres from the Turkish city of Antalya, is a particularly sensitive talking point.
Critics say the expansionism by Turkey's President Recep Tayyip Erdogan is another example of him trying to coerce others into what he wants.
Ankara says the exploration by the Oruc Reis is in response to a maritime deal signed by Greece and Egypt this month.
Turkey has also been looking for oil and gas in the Black Sea. On Friday, Mr Erdogan announced the discovery of a 320 billion cubic metre gasfield.
Turkey has traditionally relied on energy imports but Mr Erdogan vowed last week to make the country a net exporter.
Greece plans naval exercises in contested area
Greece on Monday said it would conduct a naval and air force exercise in the area of the Eastern Mediterranean that Turkey is exploring.
The live-fire exercises, due to take place south-east of Crete, would start on Tuesday and end on Thursday.
Greece had already sent a large part of its navy in response to the drilling exploration by fellow Nato member Turkey, in a dispute that also involves the EU.
The US and the EU have so far backed Greece in the dispute.
German Foreign Minister Heiko Maas is due in Athens and Ankara on Tuesday to try and revive talks between senior Greek and Turkish officials, in an initiative that started in July but was broken off by Turkey weeks later.
