According to ALJAZEERA, Turkey has slammed a "so-called agreement" between Greece and Egypt on an exclusive economic zone (EEZ) in the eastern Mediterranean Sea.
The Turkish foreign ministry in a statement on Thursday declared the deal "null and void", adding Greece and Egypt have no mutual sea border.
The area is located on Turkey's continental shelf, as reported to the United Nations, the ministry said.
It also noted that Egypt had already abandoned 11,500 square kilometres (3,352 square nautical miles) of its continental shelf in a previous agreement it signed with Cyprus in 2003.
In a televised press conference with his Greek counterpart, Egyptian Foreign Minister Sameh Shoukry said on Thursday the deal will allow Athens and Cairo to secure maximum benefits from oil and natural gas in the area.
Turkey's foreign ministry said the latest treaty sought to usurp Libya's maritime rights.
Turkey will not allow any activity in these areas and will continue to resolutely defend its legitimate rights and interests in the eastern Mediterranean as well as those of the self-declared Turkish Republic of Northern Cyprus, it added.
In a post on Twitter, Turkish Foreign Minister Mevlut Cavusoglu said: "Greece-Egypt agreement is null and void. Will continue to resolutely defend rights of Turkey&Turkish Cypriots at the table&on the ground."
Turkey said late last month it was suspending research for oil and gas exploration off a Greek island to ease tensions in the eastern Mediterranean that involved a naval presence from both countries.
Long-standing tensions between the uneasy NATO allies escalated last month after Turkey issued an advisory known as a Navtex for seismic surveys in waters between Cyprus and Crete.
French President Emmanuel Macron called for Turkey to be "sanctioned" and accused Ankara of treading on the rights of Greece and Cyprus, as all three nations scramble to exploit recently discovered gas reserves.
Relations between the European Union and Ankara have deteriorated over multiple issues, despite Turkey still formally being a candidate for membership.
As well as drilling for oil and gas off Cyprus, and support for opposite sides in the crisis in Libya, Turkey infuriated Greece and the EU earlier this year when it stopped preventing refugees from leaving for Europe, causing a surge of tens of thousands of refugees at the Greek border.
Ankara's recent move to turn the iconic Hagia Sophia, originally built as a Byzantine cathedral, back into a mosque has been the latest matter of contention, with Greece calling the move "a provocation to the civilised world".