American troops have begun pulling back from positions in northern Syria in line with an order from the White House. Turkey's President Recep Tayyip Erdogan confirmed the action hours after the White House said U.S. forces in northeast Syria would move aside and clear the path for an expected Turkish incursion.

While the U.S. move is a gift to Erdogan's government, it will be seen as a stark betrayal by the Kurds who have fought alongside U.S. forces for years to defeat the Islamic State in Iraq and Syria (ISIS). The Kurds, former U.S. officials and even some senior Republican lawmakers warned Monday that the U.S. pullout from the region could give ISIS room to rebuild, and send a message that the U.S. is willing to abandon close allies when the political winds change.

U.S. forces, "having defeated the ISIS territorial 'Caliphate' will no longer be in the immediate area," the White House said in a statement released late Sunday evening. It wasn't clear whether that meant the U.S. would withdraw its roughly 1,000 troops completely from northern Syria.

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The U.S. announcement made no mention of the fate of the Kurdish fighters who led the charge to retake the ground ISIS militants had captured in the region. The Kurds have warned for years that if their U.S. allies pulled out, they could be subjected to an onslaught by Turkish forces.

The Kurdish-led Syrian Democratic Forces (SDF) bore the brunt of the U.S.-led campaign against ISIS militants, and Republicans and Democrats alike have warned that allowing the Turks to attack the militia members would send a troubling message to American allies across the globe.

A senior U.S. security official confirmed to CBS News that U.S. forces had pulled out of observation posts at the border and pulled out of a joint patrol mechanism that was recently set up with Turkey. CBS News national security correspondent David Martin said whether the U.S. now pulls all its forces out of northeastern Syria entirely would depend on how deep the Turkish incursion is and whether the U.S.-backed SDF fight back. If they do, the U.S. official said, "the U.S. no longer has a partner in Syria."

A senior State Department official said Monday the number of U.S. troops being removed from northeastern Syria outposts was "very small," about two dozen troops, which constitute two detachments, CBS News' Christina Ruffini reports.

Turkey has threatened for months to launch a military operation to drive away Syrian Kurdish fighters from the border region east of the Euphrates River. Erdogan didn't elaborate on the planned Turkish incursion but said Turkey was determined to halt what it perceives as threats from the Syrian Kurdish fighters, who Ankara considers terrorists linked to a Kurdish separatist movement based in southern Turkey.

The senior State Department official said that the U.S. does not support Erdogan's plans, Ruffini reports. "We think this operation is a very bad idea," the official said Monday.

The official expressed skepticism about the ability of Turkey to carry out an invasion of Syria without U.S. help. The last time Turkey considered doing this it concluded that it would not be possible without U.S. air support.

The U.S. still controls airspace in northeast Syria, and it does not plan to cede this, the official said. Therefore, not only will Turkey not receive air support for its Syria operation, it will not be able to provide its own air support there.

The SDF vowed in a statement released Monday to defend itself against any Turkish attack, and noted it had sought to "avoid any military escalation with Turkey" by trying to establish a joint operation to secure a buffer zone along the border.

"We will not hesitate to turn any unprovoked attack by Turkey into an all-out war on the entire border to DEFEND ourselves and our people," SDF spokesman Mustafa Bali tweeted Saturday.

"After we fulfilled all our obligations in this regard, the American forces did not fulfill their obligations and withdrew their forces from the border areas with Turkey, and Turkey is now preparing for an invasion operation of northern and eastern Syria," the SDF command said in the statement. "This Turkish military operation in northern and eastern Syria will have a significant negative impact on our war against ISIS and will destroy any stability that has been achieved over the past years."

Despite the #securitymechanism deal and following destruction of fortifications, US forces did not fulfill their responsibilities and began withdrawing from border, leaving the area to turn into a war zone. But SDF is determined to defend NE Syria at all costs. — Mustafa Bali (@mustefabali) October 7, 2019

The U.S. announcement followed a phone call between President Trump and Erdogan, the White House said. Erdogan's office said after the call that he'd accepted an invitation from Mr. Trump to meet in Washington next month, according to Reuters.

The call came a day after Erdogan said a military operation into northern Syria was at hand and followed Ankara accusing Washington of dragging its feet on creating a "safe zone" in the region together..

Ending a war, at what cost?

The U.S. decision is a stark illustration of Mr. Trump's focus on ending American overseas entanglements — one of his key campaign promises. He alluded to that mission in a series of tweets defending the change in the Syria deployment on Monday, saying: "it is time for us to get out of these ridiculous Endless Wars, many of them tribal, and bring our soldiers home."

But his goal of swift withdrawals in Syria, Iraq and Afghanistan has been stymied by concerns from U.S. officials and American allies about the dangerous voids that would remain. As he faces an impeachment inquiry at home, Mr. Trump has appeared more focused on making good on his political pledges, even at the risk of sending a troubling signal to American allies.

In December, he announced he was pulling American troops out of Syria and was met with widespread condemnation for abandoning Kurdish allies to the Turkish assault. The announcement prompted the resignation in protest of then-Defense Secretary Jim Mattis and a coordinated effort by then-national security adviser John Bolton to try to protect the Kurds.

On Monday, Senator Lindsey Graham of South Carolina, an ally of Mr. Trump's, said in a tweet that he was still looking for the full details of the military planning, but that if the reports of a U.S. withdrawal from border positions were accurate, "this is a disaster in the making."

* Ensures ISIS comeback.

* Forces Kurds to align with Assad and Iran.

* Destroys Turkey’s relationship with U.S. Congress.

* Will be a stain on America’s honor for abandoning the Kurds. — Lindsey Graham (@LindseyGrahamSC) October 7, 2019

Graham said "if this plan goes forward will introduce Senate resolution opposing and asking for reversal of this decision. Expect it will receive strong bipartisan support."

Another close GOP ally to Mr. Trump in the Senate, Marco Rubio of Florida, said: "If reports about US retreat in #Syria are accurate, the Trump administration has made a grave mistake that will have implications far beyond Syria."

Republican Representative Liz Cheney of Wyoming also criticized the move, calling it "a catastrophic mistake that puts our gains against ISIS at risk and threatens US security."

The White House's decision "ignores lesson of 9/11. Terrorists thousands of miles away can and will use their safe-havens to launch attacks against America," said Cheney.

Separately, former senior U.S. diplomat Brett McGurk, who also left his role with the Trump administration over the president's withdrawal plans announced earlier this year, wrote a series of scathing tweets on Monday lambasting the decision to abandon the Kurds.

McGurk said the move was indicative of the current U.S. administration's "maximalist objectives for a minimalist president combined with no process to assess facts, develop options, or prepare contingencies," which he said left American troops "exposed at the slightest moment of friction."

Bottom line: Trump tonight after one call with a foreign leader provided a gift to Russia, Iran, and ISIS. FWIW, I warned of this here in @ForeignAffairs — and recommended alternatives given the hard realities on the ground and in this White House. https://t.co/QHYzI7dgEi — Brett McGurk (@brett_mcgurk) October 7, 2019

He said the pullout would leave the Kurdish factions no choice but to ally themselves with Syrian dictator Bashar Assad's Russia- and Iranian-backed regime.

At the beginning of this year, Margaret Brennan, moderator of CBS' "Face the Nation," asked Secretary of State Mike Pompeo whether Erdogan had agreed not to attack America's allies in Syria.

"The Turks have made clear that they understand that there are folks down in Syria that have their rights," Pompeo told Brennan. "We also want to make sure that those in Syria aren't attacking, terrorists aren't attacking Turkey from Syria. We're fully engaged. Ambassador Jeffrey is fully engaged in conversations with the Turks as well as with the SDF in Syria to make sure that we accomplish all of those missions. We can do each of those things."

The United States was supposed to be in Syria for 30 days, that was many years ago. 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. We quickly defeated 100% of the ISIS Caliphate,..... — Donald J. Trump (@realDonaldTrump) October 7, 2019

For his part, Mr. Trump on Monday framed the war in Syria as an entirely regional conflict, and said it would now be up to the Kurds to "figure the situation out, and what they want to do with the captured ISIS fighters in their 'neighborhood.'"

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

ISIS prisoners a threat

Mattis and other Pentagon leaders had worried that a U.S. withdrawal from northern Syria would lead to a resurgence of ISIS in the country, particularly if the SDF abandon a number of prisons holding thousands of the fighters across the region to battle Turkey.

The White House statement Sunday said Turkey would take custody of foreign fighters captured in the U.S.-led campaign against ISIS who have been held by the Kurdish forces supported by the U.S.

The prisoners include about 2,500 highly dangerous foreign fighters from Europe and elsewhere whose native countries have been reluctant to take them back, and another 10,000 or so captured fighters from Syria and Iraq.

Mr. Trump has repeatedly demanded that European countries, particularly France and Germany, take back their citizens who joined the militant organization, but CBS News' Holly Williams recently visited one of the prisons — the first U.S. network correspondent to do so — and she found at least two detainees who said they were American citizens.

There are about 5,000 prisoners at that one facility run by the SDF. The guards told Williams that many of the detainees were dangerous. They said they faced regular escape attempts, and warned that if any of the prisoners did manage to flee, they could re-join the ISIS insurgents who continue to carry out attacks in the region.

In a recently released audio recording, ISIS leader Abu Bakr al-Baghdadi called on members of the extremist group to do all they could to free detainees in jails and camps across northern Syria.

SDF commanders told CBS News last month that if foreign governments won't take their citizens back, they should help secure the prisons to prevent mass escapes, or set up an international court in Syria to try them.

It was unclear what plan Turkey might have to try and control the more than 10,000 ISIS detainees in the facilities spread across the region if the SDF forces currently running them turn their attention to fending off a Turkish incursion instead.