Tensions between Turkey and its NATO ally and neighbor Greece continued to escalate today over a collision in the Aegean Sea. Speaking on the sidelines of a NATO summit in Brussels, Greek Defense Minister Panos Kammenos accused Turkey of “provocative behavior” and declared, “It goes beyond tolerable levels.”

Kammenos’ comments followed a telephone exchange between the countries’ prime ministers late Tuesday in a bid to tamp the crisis down. Turkish Prime Minister Binali Yildirim said he told his Greek counterpart Alexis Tsipras that Greece must refrain from acts that strain ties. The Aegean should be “a sea of friendship,” he said.

The latest crisis between the traditional foes erupted when a Turkish patrol boat drove into a Greek one near the contested Kardak islets in the southeastern Aegean Sea.

A dispute over the chain of rocky outcrops, inhabited only by goats, almost dragged the countries into war in 1996. US mediation played a significant role in helping defuse the crisis but with Turkey and the United States on the brink of confrontation themselves over Syria, there is little Washington can do. Still, the issue was bound to have come up during talks between Secretary of Defense Jim Mattis and his Turkish counterpart Nurettin Canikli that were scheduled to be held in Brussels.