Turkey is at odds with Greece and the European Union over maritime rights in the Eastern Mediterranean amid a scramble for resources following the discovery of huge gas reserves in recent years.

Greece's foreign ministry formally protested to Ankara on Tuesday over its announcement that a Turkish drilling ship would conduct explorations south of the Greek island of Kastellorizo.

"Navy units have been deployed since yesterday in the south and southeastern Aegean," a Greek navy source told AFP, declining to give further detail.

The units "are ready to respond to any activity," the officer said.

An EU spokesperson said Turkey's move was "not helpful and sends the wrong message", calling for decisions about maritime rights to be "addressed through dialogue and negotiations".

"We call on Turkey to immediately cease its illegal activities, which violate our sovereign rights and undermine peace and security in the region," Greece's foreign ministry said in a statement on Tuesday.

Ankara said the location was "entirely within the Turkish continental shelf."

It signed a controversial agreement last year with Libya's UN-recognised government in Tripoli, which claimed extensive areas of the sea for Turkey.

Greece said the deal completely overlooked the maritime rights of its island Crete.

Analysts say Turkish President Recep Tayyip Erdogan used his leverage over the Libyan government -- as its main military backer -- to get the deal.

But Turkey also feels unfairly treated by rival nations in the region who have sought to exclude it from energy projects, including a huge pipeline deal between Greece, Cyprus and Israel to ship gas from the eastern Mediterranean to Europe.

Erdogan said Tuesday that Ankara's drilling moves had "foiled the traps sought to be set against Turkey in the eastern Mediterranean."

"We will uninterruptedly continue the exploration and drilling activities... in our own continental shelf" and areas licensed by the breakaway Turkish Republic of Northern Cyprus, which is only recognised by Turkey.

Relations between Brussels and Ankara have deteriorated over multiple issues, despite Turkey still formally being a candidate for EU membership.

As well as drilling for oil and gas off Cyprus, and military support for the Libyan government, Turkey infuriated Greece and the EU earlier this year when it stopped preventing migrants from leaving for Europe, causing a surge of tens of thousands of refugees at the Greek border.

Erdogan's recent move to turn Istanbul's iconic Hagia Sophia museum, a former Byzantine cathedral, back into a mosque is the latest matter of contention, which Greece called "a provocation to the civilised world".

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