BERLIN (AP) — The European Union on Friday urged Turkey to halt its drilling activities in contested waters in the Mediterranean and ordered EU officials to speed up work aimed at blacklisting some Turkish officials linked to the energy exploration.

Tensions are mounting to breaking point between Turkey and Greece over Turkey’s drilling work near the Mediterranean island of Cyprus, which like Greece is an EU member country. Turkish and Greek armed forces have been conducting snap war games in the area.

Referring to what he called “growing frustration” with Turkey, EU foreign policy chief Josep Borrell said that the sanctions — which include asset freezes and travel bans — could be extended, with Turkish vessels being deprived access to European ports, supplies and equipment. Economic sanctions are also a possibility.

EU leaders will discuss whether to impose the additional measures at a summit in Brussels on Sept 24-25 should Turkey fail to stop what the Europeans consider to be “illegal activities” in the eastern Mediterranean near Cyprus.

“Turkey has to abstain from unilateral actions. This is a basic element to allow the dialogue to advance,” Borrell told reporters in Berlin after chairing a meeting of EU foreign ministers.

He said the EU is keen to establish a “healthier relationship” with Turkey, which is a candidate for membership in the 27-nation trading bloc, although its accession talks are virtually frozen.

“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. We want to give a serious chance to dialogue,” Borrell said.

Turkey doesn’t recognize the divided island of Cyprus as a state and claims 44% of Cyprus’ exclusive economic zone as its own, according to Cyprus government officials. Turkish Cypriots in the east Mediterranean island nation’s breakaway north claim another 25%.

The Cypriot government has prepared a list of Turkish officials that it believes should face sanctions, and it is this list of names that EU officials will accelerate work on in coming days.

Cyprus was split along ethnic lines in 1974 when Turkey invaded in the wake of a coup by supporters of union with Greece. A Turkish Cypriot declaration of independence is recognized only by Turkey, which keeps more than 35,000 troops in the breakaway north.

It’s unclear whether sanctions might slow Turkey down. Steps were taken in the past — the slashing of funds meant to prepare Turkey for EU membership and the virtual freezing of its accession talks — yet Ankara has only become more vocal.

On top of that, Erdogan has shown his willingness to encourage migrants and refugees from Syria to cross the border into Greece and on to Europe, which remains deeply destabilized by the arrival of well over 1 million people in 2015, to ensure that his demands are well understood.

Turkey also plays a military role in Libya, a main jumping off point for migrants hoping to reach Europe.

Meanwhile, Greece and the United Arab Emirates began joint air force training exercises in the eastern Mediterranean, in the latest build-up of military forces. The training flights started Friday, a day after the UAE completed the transfer of nine F-16 fighter jets and four transport planes to a Greek airbase on the island of Crete, the Greek Defense Ministry said.

France, Italy, and the UAE have joined recent military exercises and training missions held by Greece and ally Cyprus, while the United States has also held separate exercises with Greece.

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Cook reported from Brussels. Derek Gatopoulos in Athens contributed.

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