Iranian officials warned the U.S. over a proposal to establish a “safe zone” in Syria, saying such a movie would be “provocative and worrisome,” according to Reuters.

The U.S. reached an agreement with Turkey for the proposed zone along the country’s northeastern border, with the two countries to establish a joint operations center.

{mosads}“Foreign Ministry spokesman Abbas Mousavi … said the recent announcements and agreements by American officials about creating a safe zone in northern Syria are provocative and worrisome,” the semi-official Fars news agency said, according to Reuters.

A U.S. delegation arrived in Turkey’s southern province of Sanliurfa last week to begin establishing the operations center, according to Ankara’s Ministry of National Defense. Turkey’s government tweeted that the work was “preliminary preparation,” saying an operation center would be up and running “in the coming days.”

The two nations have been at odds over specific details of the proposed zone, with Turkey insisting it contain no U.S.-backed Syrian Kurdish troops, which the Turkish government considers terrorists. Turkish President Recep Tayyip Erdogan has threatened to defy the U.S. and cross into Syria if Sankara’s conditions are not met.

Defense Secretary Mark Esper has said Turkish forces entering northern Syria would be “unacceptable” and that the U.S. would intervene to prevent such an incursion.