The New York Times said it obtained a memo by William Roebuck, the deputy envoy in charge of the fight against the Islamic State group, who said the United States "didn't try" stronger measures to restrain Turkish President Recep Tayyip Erdogan, although the diplomat acknowledged that the efforts may have failed anyway.
Roebuck reportedly deplored Turkey's "intention-laced effort at ethnic cleansing," which he said included abuses by Ankara's Islamist allies in Syria that "can only be described as war crimes and ethnic cleansing".
"One day when the diplomatic history is written," the newspaper quoted the memo as saying, "people will wonder what happened here and why officials didn't do more to stop it or at least speak out more forcefully to blame Turkey for its behavior."
State Department spokeswoman Morgan Ortagus declined to comment on the veracity of the "alleged private internal communications".
Roebuck, a longtime US diplomat in the Arab world who served as ambassador to Bahrain, has been in charge of on-the-ground coordination with Kurdish fighters in Syria, who bore the brunt of the US-backed campaign that crushed the Islamic State group.
"That said, we have made clear that we strongly disagreed with President Erdogan's decision to enter Syria and that we did everything short of a military confrontation to prevent it," she said.
Erdogan, who links the Kurdish guerrillas to separatists at home, launched the invasion last month after a phone call with Trump, who pulled out US troops who had effectively served as a buffer.
After outrage in Washington, Trump slapped sanctions on Turkey until Vice President Mike Pence negotiated a deal in which Kurdish fighters would withdraw from a safe zone in Syria.
Ortagus said that the United States has taken seriously alleged abuses by Turkish-backed fighters, including the killing of civilians.
"Those concerns remain and we have raised this with the highest level of the Turkish government," she said.
The report came on the same day that Roebuck's superior, James Jeffrey, arrived in Turkey for talks on Syria ahead of Erdogan's visit next week to Washington.
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