Berlin, Germany – European Union foreign ministers meeting in Berlin have agreed, “in the absence of “progress with Turkey,” to develop a list of further sanctions against the country over its recent activities in the Eastern Mediterranean, the Commission’s foreign policy chief, Josep Borrell, said on Friday.

“We are clear and determined in defending European Union interests, in solidarity with Greece and Cyprus. Turkey has to abstain from unilateral actions. This is a basic element to allow dialogue to advance,” Borrell told a press conference following the informal meeting of EU foreign ministers.

“For this reason, we must walk a fine line between preserving a true space for dialogue and at the same time showing collective strength in the defense of our common interests,” he added, saying that there is “growing frustration in the face of Turkey’s behavior.”

Borrell said that the council will seek to add the names of individuals recommended by Cyprus to face sanctions over what he described as Turkey’s “illegal drilling” in the Eastern Mediterranean, “with a view of rapid adoption.”

“We also agreed that in the absence of progress with Turkey, we could develop a list of further restrictive measures that could be discussed at the European Council next September 24,” Borrell said.

The EU official had earlier said that he would begin compiling a list of possible sanctions against individuals that could also be expanded to include Turkish assets and ships, as well as restricting Turkish access to European ports and supplies.

German Foreign Minister Heiko Maas, who has been trying to mediate a thaw between Greece and Turkey in recent weeks, also said that additional sanctions need to be discussed at the European summit in September.

The European Union is preparing sanctions against Turkey that could be discussed at the bloc’s next summit on Sept. 24 in response to the eastern Mediterranean dispute with Greece, the EU’s top diplomat said on Friday.

The measures, meant to limit Turkey’s ability to explore for natural gas in contested waters, could include individuals, ships or the use of European ports, Josep Borrell said. The EU would focus on everything related to “activities we consider illegal”, he added.

He spoke in Berlin where EU foreign ministers met to discuss support for Greece after Athens ratified a pact on its maritime boundaries to counter Turkey’s claims to energy resources in the region amid Greek and Turkish military exercises.

Borrell, who chaired the meeting, said the bloc was ready to sanction Turkish vessels, block their access to EU ports and cut off supplies. The EU could also impose sanctions on the Turkish economy.

“We can go to measures related to sectoral activities where the Turkish economy is related to the European economy,” Borrell told a news conference, referring to possible sanctions.

However, Borrell and German Foreign Minister Heiko Maas said the EU first wanted to give dialogue a chance to cool tensions between Greece and Turkey, which are NATO allies.

Turkey is also a formal candidate to join the EU, although its candidacy is also at risk and could be withdrawn as a type of sanction, diplomats have said.

The EU foreign ministers agreed to leave any decision to EU government leaders, who are set to meet for a two-day summit from Sept. 24.

“Nothing will be decided before the September European Council,” a senior diplomat said, although the envoy added that Turkey could also be rewarded with greater access to the EU’s market of 450 million consumers if it curtailed its drilling.

Greece and Turkey are at odds over the rights to potential hydrocarbon resources in the area, based on conflicting claims over the extent of their continental shelves.

Tensions escalated this month after Turkey dispatched the Oruç Reis seismic survey vessel in a disputed area following the pact between Greece and Egypt. Reuters