Deals between Turkey and the internationally recognized government in Libya on military cooperation and maritime boundaries could threaten the stability that America has “sought to encourage,” Geoffrey Pyatt, the U.S. Ambassador to the Hellenic Republic has said.

Speaking to reporters after delivering a speech at the annual Greek Economic Summit in Athens, Greece on Tuesday, Pyatt said that while the U.S. had not seen the text of the agreement, “we certainly see such a move as detracting from the situation of stability that the United States has sought to encourage.”

Already, tensions between Greece and Turkey have been on the rise over Turkey’s decision to move forward with drilling operations despite a longstanding dispute over claims to gas and oil reserves off of Cyprus.

In October, Cyprus, Greece and Egypt demanded that Turkey “end its provocative actions,” branding the nation’s oil explorations a “breach of international law.”

Pyatt’s comments on Tuesday come as Greek Prime Minister Kyriakos Mitsotakis is expected to ask fellow NATO members at the alliance’s summit this week in London to support Greece amid Turkey’s actions.

On Sunday, Mitsotakis told the ruling New Democracy party’s congress that NATO members must take action when another member “blatantly violates international law,” according to The Associated Press.

Indifference, the prime minister warned, could pose significant harm to Greece, a country still on the road to recovery from a crippling debt crisis.

Read more: newsweek