Greece has placed its military forces on high alert, recalling its naval and air force officers from holiday, as tensions with Turkey over exploration of potentially lucrative offshore energy reserves escalate in the eastern Mediterranean.

With Ankara dispatching the Oruç Reis, a drillship escorted by gunboats, to conduct seismic research in contested waters, Athens stepped up calls for Turkey to stop the “illegal” activities, intensifying a diplomatic offensive that has prompted the US, EU, France and Israel to express growing anxiety over the situation.

“Our country does not threaten [anyone], but nor can it be blackmailed,” the Greek prime minister, Kyriakos Mitsotakis, told the country on Wednesday night. “Let it be known to all: the risk of an accident lies in wait when so many military forces gather in a limited area.”

Amid the mounting international concern, Mitsotakis on Thursday thanked Emmanuel Macron, calling him a “true friend of Greece and fervent protector of European values and international law” after the French president demanded Turkey halt its explorations and said he would reinforce France’s military presence in the area.

France’s armed forces ministry confirmed it was dispatching two Rafale fighter jets and a naval frigate to the eastern Mediterranean after Macron voiced grave concern over the situation in a call with Mitsotakis the previous day.

Turkey’s prospecting should “cease in order to allow a peaceful dialogue between the neighbouring Nato members”, Macron tweeted in a strong statement, describing the situation as “preoccupying” and blaming Turkey’s “unilateral decisions” for mounting tensions.

France would “temporarily reinforce” its military presence, he said, to “monitor the situation in the region and mark its determination to uphold international law”. Last month Macron called for EU sanctions against Turkey for what he described as “violations” of Greek and Cypriot sovereignty over their territorial waters.

The EU’s foreign policy chief, Josep Borrell, described the mobilisation of naval forces as “extremely worrying” in a statement as the bloc scrambled to arrange an emergency foreign affairs council for Friday.

Greece’s foreign minister, Nikos Dendias, will also meet his US counterpart, Mike Pompeo, in Vienna on Friday for talks focusing on what Dendias described as “developments in the eastern Mediterranean in light of Turkey’s escalating violations of international legality”.

In an abrupt move, the Turkish navy issued a navigational advisory, or Navtex, early on Monday stating the Oruç Reis would be carrying out the exploratory search in the disputed area until 23 August. The communique came as the country also launched naval exercises in the region.

At the height of summer, with tourists once again heading to Greek island resorts and beaches, diplomats in Athens are eager the standoff is defused peacefully. But as warships coalesce, the spectre of conflict being triggered by a miscalculated move is also real, analysts say.

“On a scale of one to 10, I would say bilateral tensions are at a level of seven to eight,” said Constantinos Filis, a professor of international relations. “This could easily erupt into the most serious crisis between Greece and Turkey in almost 25 years. Room for human error is very real if Turkey continues on this path of revisionist brinkmanship.”

It was, he added, “simply illegal” to conduct seismic research in waters that had neither been defined by an agreement nor the verdict of an international court.

Tensions over delineation of territorial waters have long festered between Greece and Turkey. But as the dispute worsened this week, the rhetoric also went up a notch.

Dendias insisted Athens’ centre-right government would have no choice but to defend the country’s territorial integrity if maritime boundaries were breached in the race to tap regional energy reserves.

“We will not accept a fait accompli, there will be no tolerance. Greece will defend its [territorial] integrity and sovereign rights,” he said Tuesday. “We call on Turkey to leave the Greek continental shelf immediately.”

On the other side of the Aegean, the Turkish defence minister, Hulusi Akar, similarly vowed that Ankara would protect “its rights, ties and interests” in coastal areas. “Despite all this, we want to believe that common sense will prevail … it should be known that our seas are our blue homeland. Every drop is valuable,” Akar told Reuters.

Competing maritime claims have revolved around the failure of both Greece and Turkey to agree on exclusive economic zones in shared seas.

Athens maintains its islands – no matter how small – have their own continental shelves; Ankara argues that, if upheld, the Aegean would effectively be turned into a Greek lake, which, say Turkish diplomats, is utterly unacceptable to a country that sees itself as a regional power and has no intention of being left out of any energy bonanza.

The discovery of deep sea gas fields, first off Egypt and then Israel and Cyprus, has proved the eastern Mediterranean to be rich in natural resources – even if, in the case of Cyprus, hydrocarbons are still a long way from being extracted from the seabed.

Egypt and Israel have found enough gas reserves to become energy sufficient for the foreseeable future.

Last month, in an incident described as a “very near miss” by senior Greek officials, the two neighbours almost came to blows after Ankara announced it was dispatching the Oruç Reis to the same disputed area south of the Aegean isle of Kastellorizo for 10 days of oil and gas exploration. Resolution came at the 12th hour when the German chancellor, Angela Merkel, intervened, appealing to the Turkish president, Recep Tayyip Erdoğan, in a telephone call to halt the operation. Erdoğan pulled back, ordering the drillship to remain in port and agreeing to let diplomacy run its course by holding informal talks with Athens to finally settle the issue of maritime delimitations between Greek islands and mainland Turkey.

Via- The Guardian