Cyprus has branded Turkey a "pirate state" as Ankara steps up exploration drilling off the coast of the divided Mediterranean island.
"Turkey is turning into a pirate state in the Eastern Mediterranean," a statement from the Cypriot presidency said.
"Turkey insists on going down the path of international illegality."
The statement came a day after the European Union (EU) urged Turkey to drop plans to drill around Cyprus and the Eastern Mediterranean, arguing that such exploration was "illegal".
Ankara has also angered neighbouring East Mediterranean states by announcing plans to widen its exploration activities to Libyan waters.
Turkey dispatched the drillship Yavuz to conduct exploration works in a block in the south of the island.
“Our drillship, Yavuz, was relocated on [17 January] to the Block G in the south of the island in order to conduct its third drilling activity as part of the licences given to Turkish Petroleum in 2011 by the TRNC [Turkish Republic of Northern Cyprus] government,” a Turkish Foreign Ministry statement said.
Ankara urged the EU to end what it said was prejudice against Turkish Cypriots in defending its launch of the fresh round of drilling off the island nation.
Turkey ignored EU warnings last year and began drilling around Cyprus.
Cyprus's internationally recognised government discovered offshore gas in 2011, but has been at odds with Turkey over maritime zones around the island, where it has granted licences to multinational companies including ExxonMobil, Total, Shell and Eni.
Turkey says that some areas licensed by the government in Nicosia are either on the Turkish continental shelf or under the authority of the breakaway Turkish Cypriot state recognised only by Ankara.
Cyprus was divided following a Turkish invasion in 1974 after a brief Greek-inspired coup.
EU foreign policy spokesman Peter Stano said: "Concrete steps towards creating an environment conducive to dialogue in good faith are needed.
"The intention by Turkey to launch further exploration and drilling activities in the wider region goes, regrettably, in the opposite direction," he said in a statement released on Saturday.
Turkey's foreign ministry responded on Sunday: "The Turkish Cypriots have rights on this field... as much as the Greek Cypriots.
"The two sides will share the income if oil or natural gas are found there."
President Recep Tayyip Erdogan vowed on Thursday his country will step up exploration in the Eastern Mediterranean this year after signing a maritime deal with Libya.
“We will start search and drilling activities as soon as possible in 2020 after issuing licenses for the areas,” Erdogan said.
Turkey’s seismic exploration vessel Oruc Reis would soon be deployed, he added.
Earlier this month, Greece, Cyprus and Israel signed a deal to construct the EastMed pipeline to ship gas to Europe in spite of Turkey’s vehement opposition.
Turkey and Libya signed a security deal in November which was followed by the deployment of Turkish forces in the North African country.
While Turkey supports the UN-recognised government of Prime Minister Fayez al-Sarraj, countries like Egypt and the United Arab Emirates back Libyan strongman Khalifa Haftar whose forces are trying to seize the capital.