Tensions between NATO members Greece and Turkey escalated again on Saturday after Ankara launched new military drills in the eastern Mediterranean.
Greece also accused Turkish jets of an incursion as the two sides come to blows over a longstanding dispute of maritime rights and gas resources.
Both sides are staging navy drills.
In a message on NAVTEX, the international maritime navigational system, Turkey said it would carry out "gunnery exercises" from Saturday until September 11 in a zone off the southern Turkish town of Anamur, north of the island of Cyprus.
Ankara said on Thursday that military exercises would take place on Tuesday and Wednesday in a zone further east.
Greece has angered Turkey with plans to expand its coastal zone into the Ionian Sea by six nautical miles under international maritime law.
"You think we would accept such a thing?" Vice President Fuat Oktay said on Saturday, in reference to Athens's maritime border plans.
"If this is not casus belli, then what is it?" he said using a Latin term for an act or event used to provoke or justify war.
The Greek foreign ministry said in a statement on Saturday: "We urge Turkey to understand that the international law is binding for all countries of the world."
"It's not applied selectively."
Greece's national defence agency, HNDS, said Turkish fighter planes had on Friday entered the Athens Flight Information Region (FIR), the area where Greek authorities are responsible for air traffic.
The crisis has split members of the NATO alliance and in a phone call with Turkish President Recep Tayyip Erdogan on Friday, alliance chief Jens Stoltenberg urged "dialogue and de-escalation".
The EU's warning to Turkey
The European Union and Greece have called on Turkey to immediately halt energy exploration in the disputed waters.
The EU warned Turkey on Friday that it could face new sanctions if tensions do not defuse.
"The fact that the EU is appealing for dialogue on the one hand and at the same time making other plans reflects a lack of sincerity," Oktay said.
"Turkey will not hesitate to defend its interests." he added.