Turkey on Wednesday vowed to continue drilling activities off Cyprus despite tensions with the European Union, which has called on Ankara to cease its "illegal" activities.
The discovery of huge gas reserves in the eastern Mediterranean has sparked a dispute between EU member Cyprus and Turkey, which last month sent a second ship, the Yavuz, to search for oil and gas in the region.
"The drilling activities of our ship Yavuz are based on legal and legitimate grounds," the Turkish foreign ministry said in a statement.
"We reject the statement made by Greek Foreign Ministry and EU officials that deem our country's activities illegal," it added.
In May, Ankara sent the ship Fatih into Cyprus' exclusive economic zone to begin drilling there, while the Yavuz was deployed last month to search for oil and gas to the east.
The European Union said in a statement on Monday that a second attempt by Turkey to drill for oil and gas was an "unacceptable escalation", having already warned Ankara to stop its "illegal" activities or face sanctions.
The European Council said it was considering "appropriate measures" and would respond "in full solidarity with Cyprus" in light of the second exploration.
The United States and Egypt also joined a chorus of criticism this week, with Washington urging Turkish authorities "to halt these operations".
Ankara says its actions abide by international law and that it is drilling inside its continental shelf.