European Council President Donald Tusk, who chairs meetings of EU leaders, said the bloc "expects Turkey to respect the sovereign rights of EU member states" and would continue to closely monitor the situation.
His message of support at an informal summit of EU leaders in the central Romanian town of Sibiu came after Cyprus' president raised the issue. President Nicos Anastasiades described the Turkish drilling bid as "by far the most serious violation of Cyprus' sovereign rights in a very long time" and an "unprecedented escalation of illegal action" in the eastern Mediterranean.
"Essentially, these actions are tantamount to a new invasion of Cyprus by Turkey after the tragic events of 1974," he said. Turkey invaded Cyprus in 1974 in response to an abortive coup by supporters of uniting the island with Greece. A breakaway Turkish Cypriot state in the north is recognized only by Turkey. Ankara does not recognize Cyprus as a state and says part of Cyprus' exclusive economic zone falls within its own continental shelf.
Anastasiades said Turkey was "failing to live up to its obligations" as an aspirant EU member. The waters around Cyprus have huge potential and have attracted the likes of ExxonMobil, France's Total and Italy's Eni. Sizeable natural gas deposits have so far been found in three offshore areas. Cyprus says any future gas proceeds will be shared equitably with Turkish Cypriots after a deal is reached to reunify the island.
German Chancellor Angela Merkel said Anastasiades "had asked us to represent Cyprus' interests when there's contact with Turkey. We will do so." The issue of potential sanctions on Turkey was not discussed, she said.
Cypriot authorities say the Turkish drillship Fatih is anchored about 68 kilometers (42 miles) off the southwestern Cypriot town of Paphos and escorted by support ships and a Turkish navy frigate. Drilling hasn't started yet.
Turkey denies its actions are illegal and provocative. The country's foreign minister, Mevlut Cavusoglu, said earlier this week that Turkey was acting in accordance with international law and that a second drillship would be dispatched to the area.
Speaking after the summit, Greek Prime Minister Alexis Tsipras stressed the issue was "not an internal issue of Cyprus" or a bilateral issue between Cyprus and Turkey, "but a European one." "Europe's international geopolitical role cannot be credible if, first of all, it doesn't ensure the adherence to international law within itself," Tsipras said.
He said he had asked for the next summit after the European parliamentary elections between May 23-26 to tackle the issue and take whatever measures are necessary "if this unilateral provocative behavior and unilateral violation of international law continues."
Hadjicostis contributed from Nicosia, Cyprus.