As Turkish forces escalate their assault on U.S.-supported Kurdish fighters along its border with Syria, diplomatic language between the U.S. and Turkey is heating up.

Washington and Ankara give different accounts of a phone call last Tuesday between U.S. President Donald Trump and Turkey’s President Recep Tayyip Erdogan. According to a White House synopsis of the call, “[Trump] urged Turkey to de-escalate, limit its military actions, and avoid civilian casualties and increases to displaced persons and refugees.”

Turkey disputes the U.S. narrative, saying through an official, “Trump did not share any ‘concerns [about] escalating violence’ with regard to the ongoing military operation in Afrin. The two leaders’ discussion … was limited to an exchange of views.”

Turkish troops, last Monday, advanced on Afrin, a Kurdish town in northwest Syria. Information on casualties from either side is scarce. Last week, The Syrian Observatory reported hundreds displaced with 26 Kurdish fighters, 25 Syrian rebels, and 24 civilians killed so far. Turkey denies killing civilians. Turkey also accuses the U.S. of supporting forces bent on destroying Turkish security and sovereignty.

Larger geopolitical concerns are at play. Governments in Syria, Turkey, and Iraq do not want their Kurdish regions to merge into a united Kurdistan.

Helena Cobban is a Middle East analyst and writer. She’s founder and CEO of Just World Books and president of Just World Educational. Cobban will give analysis on the war along the Turkey-Syria border and Turkish fears of U.S. support for the Kurds.