U.S. Kurdish allies say President Trump's decision to pull troops from the Syrian-Turkish border is "shocking" and deflating — and they warn that the U.S. is duplicating a mistake it made in Iraq, where it has ceded partial control to Iran.

Within hours of the announcement from the White House late Sunday, local Kurdish forces on the ground confirmed to NPR that U.S. soldiers began leaving bases in Tel Abyad and Ras al Ayn, near the Turkish border.

The Syrian Democratic Forces — the blanket group that emerged four years ago, led by the Kurdish YPG as a trusted U.S. ally — reacted with deep dismay, saying it had hoped the U.S. "would fulfill its obligations to mediate a political solution from all sides to stop war."

Instead of brokering that deal, the group says, the U.S. is abruptly withdrawing. And it warns that the move will cause a new ethnic war to break out.

"There are ethnic minorities here like Armenians, Assyrians, Christians, Yazidi Kurds," the SDF says, adding, "they are all in threat of being ethnically cleansed and this in turn will not lead to any political solutions."

In a separate statement, the Syrian Democratic Forces' general command said the group "will not hesitate for a moment to defend ourselves ... to defend our country against this Turkish aggression."

The sudden U.S. turnabout was announced late Sunday, after a phone call between President Trump and Turkey's President Recep Tayyip Erdogan. As criticism rolled in Monday morning, Trump defended his decision in a series of tweets, saying the U.S. had achieved its goal of defeating ISIS.

"The United States was supposed to be in Syria for 30 days, that was many years ago," Trump said. "We stayed and got deeper and deeper into battle with no aim in sight. When I arrived in Washington, ISIS was running rampant in the area."

As his decision was criticized on Monday, Trump said in a tweet, "if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the Economy of Turkey (I've done before!)."

The president's decision to withdraw and give Turkey leeway to operate along the Syrian border is being sharply criticized by Sen. Angus King, I-Me., who calls it "morally reprehensible and strategically dumb."

By abandoning a force that fought alongside U.S. troops, King says in an interview on NPR's Here and Now, Trump is setting a dangerous precedent that could prevent potential allies from siding with the U.S. in the future.

King also says he believes Trump based his decision on a conversation with Erdogan, rather than consulting with the Pentagon, the State Department or other experts on the region.

Sen. Lindsey Graham, R-S.C., a frequent Trump ally, also criticized the president, saying on Monday, "No matter what President Trump is saying about his decision, it is EXACTLY what President Obama did in Iraq with even more disastrous consequences for our national security."

After saying the move would guarantee the reemergence of ISIS, Graham adds, "Unlike President Obama, I hope President Trump will reassess and take sound military advice."

On the subject of Turkey, Graham says he and Sen. Chris Van Hollen, D-Md., "will introduce bipartisan sanctions against Turkey if they invade Syria and will call for their suspension from NATO if they attack Kurdish forces who assisted the U.S. in the destruction of the ISIS Caliphate."

Relief groups are also worried. Any new military action in Syria could pose a new threat to 2 million civilians in Northeast Syria, says Misty Buswell, the International Rescue Committee's policy, advocacy and communications director for the Middle East.

"A military offensive could immediately displace at least 300,000 people and disrupt life-saving humanitarian services including the IRC's," Buswell said. "The IRC urges major powers to consider the humanitarian consequences of planning decisions and avoid any further unnecessary suffering of a beleaguered civilian population."

The Pentagon issued a statement around midday on Monday, clarifying that it has not endorsed a Turkish military offensive over the border.

"The Department of Defense made clear to Turkey — as did the President — that we do not endorse a Turkish operation in Northern Syria. The U.S. Armed Forces will not support, or be involved in any such operation," said Jonathan Hoffman, assistant to the Secretary of Defense for Public Affairs.

In his tweets, the president did not acknowledge the crucial contributions of Kurdish fighters in combating ISIS, protecting ethnic minorities and stabilizing a large swathe of war-torn territory other than to say, "The Kurds fought with us, but were paid massive amounts of money and equipment to do so."

Signaling that the U.S. is essentially leaving the field, Trump added that it's now up to all the other major players — naming Turkey, the Kurds and Syria, along with Iran, Iraq, Europe and Russia — to "figure the situation out." And he implied that he won't view ISIS as a priority unless the group threatens the U.S. directly.

"We are 7000 miles away and will crush ISIS again if they come anywhere near us!" Trump tweeted.

News that Turkey now plans to move ahead with an offensive along its Syrian border is also raising concerns in the U.K. and France — both of which issued statements Monday saying they're worried that a unilateral military operation could undermine the Global Coalition that assembled to fight ISIS militants.

"Daesh, which has gone underground since its territorial defeat, remains an important menace to our national security," France's Foreign Affairs Ministry says. "In Syria, the organization still has more resources and the capacity for important action."

The U.K.'s Foreign Office said that its top priority as part of the coalition is still the lasting defeat of ISIS — "and we would be concerned by any unilateral actions which may threaten the considerable progress made towards this aim."

As the potential for a clash between Turkey and the SDF rises, there are also questions about the makeup of the group. According to Amy Austin Holmes, a fellow with The Wilson Center's Middle East Program, the SDF is far more diverse than its origins as a U.S.-Kurdish pact might suggest.

"Erdogan plans to invade Syria again to destroy the SDF, who he assumes are all Kurds and PKK terrorists," says Holmes, who conducted a survey of the group in northern Syria, in a statement sent to NPR. She adds, "In reality, my survey data shows the majority of SDF are Arabs. Members of the Christian and Turkmen minority in Syria have also joined the SDF."

NPR's Ruth Sherlock, James Mastromarino and Lama Al-Arian contributed to this report.

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