The Turkish research vessel Oruc Reis, sent by Ankara to restart new exploratory activities in a region near the island of Kastellorizo, entered the Greek continental shelf early on Tuesday, state-run news agency ANA-MPA reported.
The news agency said the vessel was about 35 nautical miles south of Kastellorizo.
Oruc Reis set sail on Monday from the port of Antalya, while its global positioning system was turned off shortly before 10 a.m. on Tuesday.
German Foreign Minister Heiko Maas, who is expected in Athens on Tuesday evening for talks with the prime minister and the foreign minister on the fresh tensions in the eastern Mediterranean called on Turkey to refrain from further provocations.
"Ankara must end the interplay between detente and provocation if the government is interested in talks - as it has repeatedly affirmed," Maas said in Berlin before his flight to Cyprus and Greece.