A second Turkish ship planning to drill for oil and gas off Cyprus arrived off the Mediterranean island’s northeastern coast on Monday, triggering a strong protest from Nicosia of an infringement by Turkey of its sovereign rights.

Last month, European Union leaders warned Turkey to end its gas drilling in waters around the island or face action from the bloc, after Greece and Cyprus pressed other EU states to speak out, according to Reuters.

In a move that could further strain ties with Cyprus over exploration rights, Turkish Energy Minister Fatih Donmez was quoted by state-owned Anadolu news agency on Saturday as saying the Yavuz drillship would start drilling within a week.

Cyprus has discovered natural gas in areas rimming the south of the island in recent years, though none has been extracted.

Refinitiv Eikon shipping data showed the Yavuz arrived off Cyprus overnight.

A strongly-worded statement issued by the Cypriot presidency accused Turkey of a “grave violation” of the sovereignty of the island. “This planned second drilling … is an escalation by Turkey of its repeated violations of Cyprus’s sovereign rights based on the U.N. Law of the Sea and international law, and is a most serious violation of the sovereignty of the Republic of Cyprus,” Cyprus’s presidency in Nicosia said in a statement.