U.S. Defense Secretary Jim Mattis was optimistic on Thursday about finding “common ground” with Turkey in Syria, where Turkish troops and their local allies may be positioning for a strike against territory occupied by American troops.

Wherever that “common ground” might be, there will evidently be no Kurds standing upon it, as Turkey has demanded the expulsion of Kurdish fighters from America’s coalition in Syria.

Mattis, who was in Brussels to attend a meeting of NATO defense ministers, said the reality of Turkey’s differences with U.S. policy in Syria was less dramatic than the rhetoric surrounding it.

“I believe we are finding common ground and there are areas of uncommon ground where sometimes war just gives you bad alternatives to choose from,” he said after speaking with Turkish Defense Minister Nurettin Canikli.

The worst of those bad alternatives would involve Turkey pushing past Afrin region in Syria to attack Manbij, where both American troops and Kurdish forces unambiguously allied with the United States against the Islamic State are positioned. Turkish officials, notably including President Recep Tayyip Erdogan, have been telling the United States to pull its troops out so Turkey can have a clean shot at the Kurds. U.S. officials have steadfastly refused to do so.

After his meeting with Mattis, Canikli said he presented the American defense secretary with documents proving “organic” links between the YPG and the PKK and asked the United States to remove the Syrian Kurdish fighters from the Syrian Democratic Forces (SDF).

Turkey believes these Syrian Kurdish militia groups are allied with the violent PKK separatist party inside Turkey, and harbor long-term plans to create a new cross-border Kurdish state that would consume portions of Turkey, Syria, and Iraq. Ankara has implicitly, and sometimes explicitly, described this possibility as a worse threat to Turkish security than ISIS, and has used highly intemperate language to accuse the United States of supporting terrorists by standing with the Kurds.

Erdogan did so again on Tuesday, offering a public warning to the American people that their money is being used to support terrorism by funding the Kurdish YPG militia in Syria.

Presented with a warning from American generals that U.S. troops in Manbij will defend themselves if attacked, Erdogan retorted, “Those who say ‘if they hit us we will respond harshly’ have clearly never received an Ottoman slap.” His threat was literally laughed off by U.S. State Department spokeswoman Heather Nauert, a response that is unlikely to placate the Turkish president.

Secretary of State Rex Tillerson himself arrived in Ankara on Thursday to meet with Erdogan in a three-hour session whose only other participant was Turkish Foreign Minister Mevlut Cavusoglu, who served as translator. Tillerson declined to comment on the meeting afterward, instead pledging to hold a joint news conference with Cavusoglu on Friday.

Prior to his meeting with Erdogan, Tillerson stressed that the U.S. and Turkey share common objectives to “defeat ISIS, to defeat terrorism, to reduce the violence, protect people and support a peaceful resolution to the conflict in Syria.”