BRUSSELS — European Union leaders early Friday gave the green light for the expansion of sanctions against Turkey over its exploration of gas reserves in Mediterranean waters claimed by EU members Greece and Cyprus.

"Regrettably, Turkey has engaged in unilateral actions and provocations and escalated its rhetoric against the EU, EU member states and European leaders," they said in a statement from their summit in Brussels.

At their last summit in October, the leaders offered "a positive political EU-Turkey agenda" to Ankara, including trade and customs benefits and the prospect of more funds to help Turkey manage Syrian refugees on its territory if it halts its "illegal activities" in the eastern Mediterranean.

The leaders said that offer remains on the table if Turkey is prepared to enter into a "genuine partnership" and begin a real dialogue with the EU, and if Ankara shows a willingness to resolve differences through dialogue and in accordance with international law.

But given the lack of a response so far, they invited the 27-nation bloc's ministers "to adopt additional listings" for sanctions "concerning restrictive measures in view of Turkey's unauthorized drilling activities in the Eastern Mediterranean."

The leaders told EU foreign policy chief Josep Borrell to draw up a report on the state of EU-Turkey political, economic and trade relations and to suggest how to proceed, including on widening sanctions, and submit it to the leaders by the time they hold their summit in March next year.

Pressure had been mounting for the EU to act, given its previous threats and Turkey's refusal to respond.

"The stakes are very precise, very clear: the credibility of the European Union," Greek Prime Minister Kyriakos Mitsotakis said ahead of the meeting. He recalled that the leaders said in October that there would be consequences if Turkey "continued its delinquent behavior."

"So now, it will be seen whether, as Europe, we are really credible in what we ourselves have agreed to," Mitsotakis said. 

The 27 EU countries are split over how best to handle Turkey. France and Cyprus have pushed for tougher measures like economic sanctions, but other countries are concerned about further undermining the country's already ravaged economy and destabilizing the region.

On Wednesday, Turkish President Recep Tayyip Erdogan brushed off the threat of sanctions and accused the EU, which Turkey is a candidate to join although its membership talks are blocked, of acting "dishonestly" and failing to keep its promises.

"Any decision to impose sanctions against Turkey won't be of great concern to Turkey," Erdogan told reporters. 

Just over a year ago, the EU set up a system for imposing travel bans and asset freezes on people, companies or organizations linked to drilling activities "which have not been authorized by the Republic of Cyprus, within its territorial sea or in its exclusive economic zone or on its continental shelf."

Two officials are currently on the list: the Vice-President of the Turkish Petroleum Corporation and the deputy director of its Exploration Department. The idea is to add more people or some organizations to the list.

It's unclear anyway whether more sanctions would 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 into 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 in Africa for migrants hoping to reach Europe.