BEIRUT — Residents of northeastern Syria were bracing Thursday for the fallout of President Trump’s unexpected move to withdraw U.S. troops, a decision that many in the region regard as a betrayal that will reverberate well beyond this corner of Syria.

With Turkey threatening to invade from the north, the Syrian government threatening to retake the area by force and the Islamic State regrouping in their midst, Kurds and Arabs were unsure — and divided — over what most to fear next.

In the Syrian town of Kobane, where the United States’ alliance with Syria’s Kurds began in 2014, thousands of Kurds marched in anger and dismay toward a U.S. military base, many clutching photographs of their children killed fighting the Islamic State alongside U.S. forces. They urged Trump to reverse his decision.

“She died beside Americans, and now that you are leaving, I will also die,” shouted a mother holding up the photograph of her dead daughter, who had served in a women’s unit of the main Kurdish militia, according to witnesses.

The decision represented yet another setback to Kurdish aspirations for some form of statehood, which have repeatedly met disappointment at the hands of the United States. The letdowns began after President Woodrow Wilson pushed for but failed to secure a separate Kurdish state at the 1919 peace conference following World War I, which drew the borders of the modern Middle East.

Kurds say the hopes they have since placed in the United States have continued to be dashed. In 1975, the United States abandoned support for a Kurdish uprising in Iraq after President Saddam Hussein struck a deal with their ally, the Shah of Iran. In 1991, President George H.W. Bush encouraged Iraqis to rise up against Saddam, but when Kurds in the north and Shiite Arabs in the south responded to the call, the U.S. military refrained from going to their aid. Most recently, the Trump administration last year withheld support for an independence referendum in Iraqi Kurdistan, and Iraqi troops rolled unopposed into areas the Kurds had controlled.

“There is a big disappointment, especially as the threats against us are so huge,” said Hoseng Hesen, a Syrian-Kurdish journalist who attended the march and provided an account of what took place.

This latest betrayal has ramifications far beyond the aspirations of Kurds, said Hoshyar Zebari, the Kurdish former foreign minister of Iraq.

“This sudden change in policy is worrying not only to Syrian Kurds but to all the U.S. allies in the region,” he said. “The message it sends is that there really is a question of trust. This will cause many governments to rethink their alliances with a superpower that can really can just abandon them and leave them in the lurch and throw them under the bus.”

Russia, Turkey and Iran will be the biggest beneficiaries, he said. “These are the new powers in the Middle East. Why should we oppose them? Why should we antagonize them?” he asked.

Kurds living in predominantly Kurdish towns and villages strung out along the northern Syrian border said their biggest concern was the continuing threat of a Turkish incursion.

The prospect of Turkish invasion may have played a part in prompting Trump’s move to withdraw troops. Trump announced the decision after speaking on the telephone Friday with Turkish President Recep Tayyip Erdogan, who has long been hostile to American support for the new Kurdish entity emerging along Turkey’s border.

For weeks, the Kurds have been digging trenches around the towns adjoining Turkey, as a means of defense against the Turkish troops massed on the other side of the border. It was unclear whether Trump’s decision to pull out the troops and his conversation with Erdogan would delay, prevent or encourage a Turkish military operation.

Turkish officials reiterated their threat Thursday. “They can dig tunnels or ditches if they want. They can go underground if they want. When the time and place come, they will be buried in their ditches,” Turkish Defense Minister Hulusi Akar was quoted as saying by Turkey’s official Anadolu news agency, during a visit to Qatar.

The Syrian Kurds are now hoping to revive negotiations with the Syrian government on a deal that would enable them jointly to confront Turkey, said Salih Muslim, a spokesman for the main Kurdish political body, the People’s Democratic Union, or PYD.

“We are open to all to all kinds of dialogue with everybody and we didn’t close our doors,” he said. “We are ready to discuss it and have a dialogue.”

The Syrian government has proved less willing, however, he said.

Arabs who joined the Kurdish-led Syrian Democratic Forces are also feeling betrayed, said Omar Abu Layla, a Syrian Arab with the activist news network Deir al-Zour 24. The SDF is an umbrella for Kurdish and Arab forces created by the United States in 2015 to provide military aid without alienating Turkey, which regards the Kurdish component of the force as a terrorist group.

Most of the Arabs in the force have fought both the Syrian government and the Islamic State, and they fear a return of either one, he said. Arabs who joined the SDF feel a sense of “shame” at having aligned with a power that is now abandoning them, he said. Many are considering leaving the battle against the last pocket of Islamic State territory in southeastern Syria rather than continue to risk their lives in the fight without U.S. support.

Kurds may also abandon the fight, Kurdish officials said. No decision has been reached, Muslim said, but if Turkey continues to threaten an incursion, it is likely, he said, that many fighters will leave the front lines in the fight against the Islamic State to defend their homes in the north against Turkey.

Muslim said the Kurds are urging the United States at least to sustain the air support that has proved instrumental in driving the Islamic State back from the vast areas of Syria the militants once occupied. The Kurds are hoping, he said, for the United States to declare a no-fly zone over the area similar to the one it imposed over Iraqi Kurdistan in 1991. That no-fly zone deterred the advance of Saddam’s forces into the Kurdish areas of Iraq and enabled the flourishing of an autonomous Kurdish region.

Fears of an Islamic State resurgence is widely shared across the region.The SDF warned Thursday that the withdrawal of U.S. troops will facilitate a revival of the militants, who have been regrouping and maintain sleeper cells across the area.

“The final defeat has not yet been achieved. It is at a crucial and critical stage that requires concerted efforts by everyone, and greater support to all combat forces on the ground, not withdrawal,” the SDF said in a statement on Trump’s decision.

“Withdrawal under these circumstances will lead to instability and insecurity, creating a political and military vacuum, leaving its people between the claws of hostile forces and groups,” it added.

Ghalia Alawani in Beirut contributed to this report.

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