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WASHINGTON (AP) — A senior American diplomat has written a highly critical assessment of the Trump administration's abrupt withdrawal of troops from northeast Syria last month, a decision that paved the way for an attack on U.S.-allied forces in the area, officials said Thursday.

In an internal memo, William Roebuck, the top American diplomat in northern Syria, takes the Trump administration to task for not doing more to prevent Turkey's invasion or protect the Kurds, who fought alongside U.S. forces in the battle against the Islamic State group, according to two U.S. officials familiar with the matter.

One of the officials described the memo, which was obtained and first revealed by The New York Times, as "lengthy and harsh." The officials were not authorized to discuss internal documents publicly and spoke on condition of anonymity.

Roebuck's memo highlights how Trump's decision to withdraw American troops was deeply divisive, even within his own administration. The move was widely criticized by Democrats and Republicans as abandoning a key ally in the fight against the Islamic State.

Turkey invaded days after President Donald Trump ordered the small number of U.S. special forces in the area to leave.

In the memo quoted by the Times, Roebuck said there was no way to know if more pressure on Turkey's president, Recep Tayyip Erdogan, would have stopped the operation.

"It's a tough call, and the answer is probably not. But we won't know because we didn't try," the Times quoted Roebuck as writing.

He also raised concerns about the possibility that Turkish-backed militias taking part in the operation were undisciplined and could commit atrocities amounting to war crimes.

Roebuck, a top deputy to the U.S. special envoy for Syria, James Jeffrey, said the withdrawal of U.S forces had badly, if not irreparably, damaged the trust of the Kurds. The memo was sent to Jeffrey and a number of other officials who deal with Syria policy.

Jeffrey is in Ankara, Turkey's capital, for discussions with the Turks on putting in place an Oct. 17 deal negotiated by Vice President Mike Pence that created a buffer zone along portions of the Turkey-Syria border. On Wednesday, a senior U.S. official said Jeffrey was raising concerns about alleged war crimes.

Trump's ordered withdrawal from the northeast has been somewhat tempered by the deployment of forces to protect oil fields in Kurdish-held areas, some of which are vulnerable to attacks by IS, Roebuck wrote in the memo. But he also said those deployments would play into long-held beliefs in the Mideast that the U.S. is only interested in the region for its oil.

The State Department declined to confirm or deny the existence of Roebuck's memo, but offered a long statement defending the administration's actions that tacitly admitted there is robust internal debate on Syria policy.

"No one can deny that the situation in Syria is very complicated and there are no easy solutions and no easy choices," spokeswoman Morgan Ortagus said. "This administration's job is to do what is best for U.S. national security and the American people."

The Associated Press