Turkey's decision may have been a calculated risk, analysts say, as it looks to secure greater influence and energy resources in territory it claims as its own, and to counter what it sees as increasing encroachment by Cyprus and regional rivals.
Already tense over divided Cyprus, the eastern Mediterranean has become increasingly sensitive after the discovery of potentially huge oil and gas reserves drew the United States, Greece, Egypt and Israel into an increasingly complex landscape.
As it edges away from the EU, Ankara may now see European sanctions as less of a risk. And relations with the US are already frayed over multiple issues.
The offshore area where the Turkish ships Fatih and Yavuz are exploring for gas is part of EU-member Cyprus's exclusive economic zone where it has invited Western giants like ExxonMobil and France's Total to drill in lucrative deals for Nicosia.
That has riled Turkey, which backs the Turkish-speaking north of divided Cyprus, and claims the offshore area as part of its own continental shelf.
Turkey says its drilling is within international law and that Nicosia's registered economic zone is not recognised by the north's Turkish Cypriots.
Part of the Turkish move may be prompted by increasing energy cooperation between Cyprus, Greece, Israel and Egypt.
"Beyond energy, this has to do with the power projection that Turkey is trying to introduce in the region," said Harry Tzimitras, director of the PRIO Cyprus Centre think tank.
He added Turkey felt the need "to make itself heard".
The EU has repeatedly lambasted Turkey over "illegal" drilling and last month threatened Ankara with sanctions if it did not stop.
But President Recep Tayyip Erdogan defends Turkey's activities, as one of the guarantors of Cyprus' independence along with Greece and Britain, and has lashed out at outside actors for what he called interference.
This week he said their "noise" would not deter Turkey from its goal.
Cyprus has been divided between the Republic of Cyprus and a northern third under Turkish military control since 1974 when Turkey invaded in response to a coup by a Greek military junta.
Current tensions over gas drilling are also likely related to the collapse of peace talks in 2017, experts say.
While negotiations to reunify the island have not restarted, Cyprus has moved to start gas and oil exploration by issuing licences.
Even with rising tensions, few see the possibility of an armed conflict. Both sides are keen to avoid an escalation despite the rhetoric.
But Turkish pro-government newspapers say naval vessels and drones are providing protection to the drilling ships, just in case.
In February, Turkish warships blocked the path of a drill ship contracted by Italy's ENI, forcing its mission to be abandoned.
"All parties will refrain from military clashes, even if there is still a risk of an accident," said Ozgur Unluhisarcikli, the Ankara director of the German Marshall Fund of the United States think tank.
The EU could slap "symbolic" sanctions on Turkey, but not any measures that could hurt the Turkish economy, he added.
The EU's "allure" and influence on Turkey is waning, said Tzimitras. "Losing the EU is not as important as it was in the past."
Ankara has warned against sanctions, which Foreign Minister Mevlut Cavusoglu said this week would "backfire".
While the US has called for drilling to stop, Unluhisarcikli said Washington was unlikely to punish Ankara over gas exploration as it is already eyeing sanctions over a Russian S-400 missile defence system deal.
Energy and beyond
Cypriot Energy Minister George Lakkotrypis last month said Cyprus would earn an estimated $9.3bn over 18 years from exploiting its Aphrodite gas field under a contract with Shell, US-based Noble and Israel's Delek.
Turkey itself granted exploration licences to Turkish Petroleum in 2009 and 2012. For now, Ankara buys gas mainly from Russia, Iran and Azerbaijan.
The size of the reserves and their future potential are unclear, but analysts say Turkey's actions offshore are more focused at boosting its regional influence and countering Cyprus.
"What Turkey is doing is not in the perspective of economic gains, Turkey is doing this to disrupt the plan of the Republic of Cyprus," Unluhisarcikli said.
Ankara this week slammed Greece as a "spoiled child" of Europe and Cyprus as its "hellion", adding that being an EU member did not give Nicosia the right to "usurp legitimate rights and interests of the Turkish Cypriots".