Greece is pressuring the European Union to consider suspending the EU’s customs union agreement with Turkey in retaliation for its controversial exploration activities in the East Mediterranean.

Greece’s Foreign Minister Nikos Dendias has written to the European commissioner for neighbourhood and enlargement, Oliver Varhelyi, asking him to look at the measure in response to Turkey’s "repeated violations of the agreement".

The Greek move comes after Turkey said last week it was sending back seismic vessel Oruc Reis to resume controversial exploration.

The Turkish Navy said the vessel will conduct seismic activities until 22 October, lowering expectations of a negotiated settlement to overlapping maritime claims soon.

Oruc Reis is deployed south of the Greek island of Kastellorizo, escorted by two other Turkish naval vessels.

Turkish President Recep Tayyip Erdogan has angered EU members Greece and Cyprus by stepping up seismic and drilling work in disputed waters in the East Mediterranean.

Turkey’s Foreign Ministry said the activities were “fully within the Turkish continental shelf".

“It is unacceptable for there to be opposition against our country, which has the longest coastline in the eastern Mediterranean, operating 15 kilometres from its mainland,” it said, adding that Greek criticisms were “baseless accusations with no standing in international law”.

“Our expectation from Greece is for it to withdraw its maximalist claims that are contrary to international law and enter into a sincere dialogue with us,” the ministry said.

EU leaders condemned Turkey’s “unilateral actions and provocations” in the Mediterranean last week. The US also denounced Ankara's controversial drilling and seismic work.

The bloc is now threatening to consider sanctions on Turkey at its next summit in December unless Ankara opts for diplomacy.

Germany has been spearheading diplomatic efforts to help reconcile NATO members Turkey and Greece, which have a long history of border disputes and competing claims over maritime rights.

At the same time, Turkey has deterred international companies from drilling off Cyprus, where it supports the Turkish Republic of Northern Cyprus.