Greece's navy has deployed ships in the Aegean Sea in "heightened readiness" over Turkish energy exploration activities, a navy source said Wednesday.

The move came after the Greek foreign ministry on Tuesday formally protested to Ankara following the announcement that a Turkish drilling ship would conduct explorations in the area south of the Greek island of Kastellorizo in the southeastern Aegean.

"Navy units have been deployed since yesterday in the south and southeastern Aegean," the source told AFP, declining to give further detail. The units "are ready to respond to any activity," the officer said. The Greek navy also called on seafarers to ignore a maritime restriction in the area issued by Turkey.

Prime Minister Kyriakos Mitsotakis has called separate meetings with Greek party leaders on Thursday and Friday to brief them on "national issues," his office said. Athens had said Turkish surveys in a section of the Greek continental shelf escalate tensions in a region where Turkey disputes Greek maritime rights. "We call on Turkey to immediately cease its illegal activities, which violate our sovereign rights and undermine peace and security in the region," the Greek foreign ministry said.

The EU in general is unhappy at what it says is Turkey's illegal drilling for oil and gas off the coast of Cyprus, as well as Ankara's actions in support of the UN-recognised government in Libya. There is also widespread concern at the direction Turkey -- still nominally a candidate to join the EU -- has taken under President Recep Tayyip Erdogan, with the decision to turn Istanbul's iconic Hagia Sophia cathedral from a museum into a mosque the latest source of contention.

Erdogan went ahead with the plan despite appeals from the United States and Russia and condemnation by France and Pope Francis, while Greece's culture ministry has called the move "a provocation to the civilised world".