ATHENS, Greece (AP) — Greece accused neighbor Turkey of undermining efforts to ease a crisis over drilling rights in the eastern Mediterranean on Monday, after Turkey announced its survey vessel would be dispatched for a new research mission in disputed waters.

The move threatened to reignite a spat over sea boundaries in an area between Greek islands, Cyprus and Turkey’s southern coast which had flared up over the summer, prompting a military build-up and fears of a confrontation between the two NATO members.

The state-run Anadolu Agency said the Turkish search vessel, Oruc Reis, left the port of Antalya on Monday, to resume its survey of hydrocarbon resources in the eastern Mediterranean. A international maritime safety advisory, or Navtex, issued late Sunday said the exploration would last until Oct. 22.

Greece’s Foreign Ministry on Monday called the decision a “major escalation and a direct threat to peace and security in the region.”

Ankara and Athens had earlier this month agreed, under NATO’s auspices, to set up a system to avoid potential military conflicts and accidents, including a hotline.

The two countries had also agreed to resume so-called exploratory talks aimed at building confidence and resolving disputes which were last held in 2016.

The Turkish vessel's return comes a day after Turkey's Foreign Ministry issued a statement accusing Greece of “insincerity” for what it said was Athens' continued actions to raise tension while declaring itself to be ready for a dialogue. Among other things, the Turkish Foreign Ministry accused Greece of declaring military exercises in the Aegean Sea to coincide with Turkey's Oct. 29 national day celebrations. Turkey retaliated by declaring exercises on Oct. 28, the statement said.

Turkish Defense Minister Hulusi Akar said the Orus Reis was continuing with its “planned and scheduled activities,” adding that the Turkish navy would provide “support and protection” if necessary.

Energy Minister Fatih Donmez tweeted that the Orus Reis had raised its anchor to “take the X-ray” of the Mediterranean seabed, after the completion of maintenance work.

Turkey had announced last month that it was pulling the Orus Reis to shore for maintenance and resupply, saying the move would give “diplomacy a chance.”

Turkey faces the threat of sanctions from the European Union, which has sided in the dispute with member states Greece and Cyprus.

Suzan Fraser reported from Ankara, Turkey.