Turkey on Friday called on the European Union to act as an `honest mediator' in its dispute with EU members Greece and Cyprus over the exploration of gas reserves in the Mediterranean, after European leaders approved expanding sanctions against Ankara.

The leaders said early Friday that Turkey _ which is a candidate to join although its membership talks are blocked _ has ``engaged in unilateral actions and provocations and escalated its rhetoric against the EU.'' This was despite the fact that they had offered trade and other incentives to Turkey to halt its activities during their last summit in October, they said.

The leaders tasked EU foreign policy chief Josep Borrell with drawing up a report on the state of EU-Turkey political, economic and trade relations and to suggest how to proceed, including on widening sanctions. Borrrell was asked to submit the report to the leaders by the time they hold a summit in March.

Turkey's Foreign Ministry slammed the EU decision, saying Ankara rejects the 27-member group's ``biased and unlawful attitude.''

A ministry statement said the decision to expand sanctions against Turkey was approved out of solidarity with Greece and Cyprus. The two countries' alleged misuse of the solidarity and veto rights had thrust EU-Turkey ties into a ``vicious circle,'' it said.

``The situation is harming the joint interests of Turkey and the EU as well as our region's peace, security and stability,'' the ministry said. ``The EU should take up the role of an honest mediator, it must act in a principled, strategic and sensible manner.''

Tensions between NATO allies Turkey and Greece escalated over the summer with a military build-up after Turkey sent its seismic survey vessel Oruc Reis, escorted by navy frigates, into disputed waters. The move prompted Greece to also send its warships, and both countries conducted military exercises to assert their claims.

Late last month, Oruc Reis returned to port, as it had done before October's EU meeting. However, another research ship, the Barbaros Hayreddin Pasa, remains off Cyprus' southwestern coast.

Turkey says it is standing up for its energy rights, as well as those of breakaway Turkish Cypriots, while Athens and Nicosia call Turkey's actions an illegal incursion into areas where they have exclusive offshore exploitation rights.

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.

Last year, the EU set up a system for imposing travel bans and asset freezes on people, companies or organizations linked to contested drilling activities. Two Turkish Petroleum Corporation officials are already on the list, and the leaders say those sanctions should be broadened.

The EU decision comes as Turkey is also faced with the prospect of U.S. sanctions over its purchase of a Russian air defense system which has already resulted in the NATO-member country being kicked out of the U.S. F-35 stealth fighter program.