European officials on Thursday warned Turkey against pursuing a survey mission looking for gas reserves near Greek islands in the eastern Mediterranean.

Greece and Cyprus have accused Turkey of undermining their sovereignty by continuing to pursue energy resources within their territorial waters.

"The government is underlining to all parties that Greece will not accept a violation of its sovereignty and will do whatever is necessary to defend its sovereign rights," said Greek government spokesman Stelios Petsas.

French President Emmanuel Macron has called for sanctions against Turkey, saying it is "not acceptable for the maritime space of a European Union member state to be violated or threatened."

Last year, the EU adopted a sanctions regime targeting Turkey over its unauthorized gas drilling in Cypriot waters.

The instrument provides the EU with a way "to sanction individuals or entities responsible for, or involved in, unauthorized drilling activities of hydrocarbons in the eastern Mediterranean," according to a statement by EU foreign ministers in November.

Read more: Turkey's maritime claims in the Mediterranean Sea raise thorny legal questions

Turkey defiant

However, Turkey has rejected claims that its energy-related activities in the region are transgressing Greek or Cypriot sovereignty. Instead, the Turkish government has claimed that it is well within its right — or those of Turkish Cypriots — to explore areas claimed by Cyprus and Greece.

"We want all natural resources in the eastern Mediterranean to be shared fairly," said Turkish presidency spokesman Ibrahim Kalin. "We will never accept threats or sanctions. We do not accept Greece's maximalist position."

Turkish survey ship Oruc Reis's mission remains "valid and effective," according to the port in which it is currently anchored off of. Its mission is likely to run through to August 2.

US officials have chided Turkey for pursuing the mission despite several warnings.

"I want to echo the clear message from Washington and elsewhere in Europe, urging Turkish authorities to halt operations that raise tensions in the region, such as plans to survey for natural resources in areas where Greece and Cyprus assert jurisdiction in the eastern Mediterranean," said US Ambassador to Greece Geoffrey Pyatt.

lws/stb (AFP, Reuters, AP)