Turkey said Sept. 1 that its Oruc Reis exploration vessel will carry out seismic surveys in a disputed area of the eastern Mediterranean until Sept. 12, provoking an angry response from neighboring Greece.

Turkey and Greece, NATO allies, disagree over claims to hydrocarbon resources in the area based on conflicting views on the extent of their continental shelves in waters dotted with mostly Greek islands.

Both sides have held military exercises in the east Mediterranean, highlighting the potential for the dispute over the extent of their continental shelves to escalate.

The Turkish navy issued an advisory saying the Oruc Reis would continue working until Sept. 12. It had previously been scheduled to work until Sept. 1.

The advisory came after the European Union’s executive earlier on Aug. 31 called for dialogue with Turkey and demanded that Ankara refrain from unilateral steps that stoke tensions in the eastern Mediterranean.

Greece’s foreign ministry called the advisory illegal and urged Turkey to ease tensions and work for stability in the region.

“Turkey continues to ignore calls for dialogue and to escalate its provocations,” the ministry said in a statement. “Greece won’t be blackmailed.”

Greece will keep seeking maritime deals with its neighbors in the region, based on international law and the law of the Sea, the ministry added. Last week, Greece ratified an accord on maritime boundaries with Egypt.

Turkey’s latest advisory referred to a specific exploration area. On Aug. 29, Turkish Foreign Minister Mevlut Cavusoglu said the Oruc Reis would continue working for the next 90 days as it moved gradually closer to the Turkish province of Antalya.

Seismic surveys are part of preparatory work for potential hydrocarbon exploration. Turkey has also been exploring for hydrocarbon resources in the Black Sea and discovered a 320 billion cubic meter (11.3 trillion cubic feet) gas field.

Separately, Turkey also said it will hold a military exercise off northwest Cyprus until Sept. 11.

Offshore