This file photo taken on August 23, 2019 in Istanbul shows a view of Turkish General Directorate of Mineral research and Exploration's (MTA) Oruc Reis seismic research vessel docked at Haydarpasa port, which searches for hydrocarbon, oil, natural gas and coal reserves at sea. (AFP)
In a move reviving tensions with Greece, Ankara sent the Oruc Reis vessel to a disputed area near the Greek island of Kastellorizo off Turkey's coast on Monday.
Greece said it was a "major escalation" of their dispute over maritime rights and claims to hydrocarbon resources in the region.
"Oruc Reis has reached the area in the eastern Mediterranean where it will carry out its activities. Tests began yesterday and we are beginning to receive the first seismic readings today," Fatih Donmez, the Turkish energy minister, told a conference by video link.
Turkey had withdrawn the vessel from contested waters in the region last month to "allow diplomacy" before an European Union summit at which sanctions against Turkey were discussed.
On Tuesday, the United States slammed Turkey's decision to send the vessel back, accusing Ankara of unilaterally stoking tensions and "deliberately" complicating the resumption of talks with Greece.