Russia and Turkey are now poised to further derail the US's limited presence through a mutual agreement.

The two countries announced on Wednesday that Russian military police and Syrian border guards would "enter" the Syrian border, beyond the area Turkish forces have assaulted, to remove Kurdish groups.

Brett McGurk, the former US envoy to the anti-ISIS coalition, said Trump "seems not to realize the extent to which the entire position in NE Syria has unraveled" and questioned the safety of US troops.

"How would a small residual US force be sustained without land supply," McGurk said. "Extremely difficult and high risk."

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Turkish President Recep Tayyip Erdogan and Russian President Vladimir Putin walked out of a bilateral meeting in the Black Sea resort town of Sochi, Russia, on Tuesday having taken shots at the US's expense and achieving their goal of evicting the US from northern Syria.

Now Russia and Turkey are poised to further derail the US's limited presence with a mutual agreement.

The two leaders unveiled a memorandum of understanding to "reiterate their commitment to the preservation of the political unity and territorial integrity of Syria" in the wake of President Donald Trump's abrupt withdrawal of US troops from the region earlier this month.

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Turkey and Russia have long advocated for the withdrawal of US troops from Syria. Turkey, which sees US-backed Kurdish forces operating along its border with Syria as a national-security threat, forced Trump's hand to withdraw troops from the area when it launched an offensive, according to the Trump administration.

Ankara, Turkey's capital, and Moscow announced that Russian military police and border guards from Syria, Russia's strongest ally in the Middle East, would jointly "enter" the Syrian border, beyond the area Turkish forces initially assaulted, to remove Kurdish groups within six days.

US vehicles withdrawing from northern Syria on October 21. Reuters

"The situation on the eastern bank of the Euphrates raises some flags," Russian Foreign Minister Sergey Lavrov said on Tuesday, referring to US military presence. "It is in that area beyond the control of the [US] and the US-led coalition have been actively creating comfortable accommodations, complete with electricity and water supplies and social and health services. Moreover, they were not even hiding that they wanted to create a quasi-state there."

"I am sure that the implementation of this memorandum will strongly interfere with these plans," Lavrov added. "In the final analysis, we will work to nullify them."

Brett McGurk, the former US envoy to the anti-ISIS coalition, said Trump "seems not to realize the extent to which the entire position in NE Syria has unraveled."

"Under the Putin-Erdogan deal, the Syrian regime will take control of the main border crossings with the Iraqi Kurdistan Region at [Faysh Khabur] and Rabiya," McGurk said on Twitter, referring to vital towns that border Syria, Iraq, and Turkey.

Faysh Khabur, a strategically located town on the borders of Syria, Iraq, and Turkey. Google Maps

"Putin and Erdogan want us out," McGurk added. "That's been their plan for some time. What they agreed to yesterday makes it very difficult to realistically maintain a US presence, let alone one that might meaningfully impact the situation on the ground in Syria or against ISIS."

McGurk, who resigned in December, citing Trump's "complete reversal" of US policy that came as a "shock," also said the small number of special-operations forces still in the region would face logistical complications after the military campaign.

Trump announced he would keep a small military contingent in Syria to protect oil fields, a goal Trump's backers have advocated for, but which confused some military officials: "I don't know where all this oil infrastructure stuff is coming from," a senior US official said to Al-Monitor. "Maybe playing to what [Trump] wants here. We have not seized the oil fields."

"How would a small residual US force be sustained without land supply," McGurk said. "Extremely difficult and high risk. In military affairs, you don't preserve options after making a catastrophic decision without thought or preparation. You foreclose them, as last three weeks demonstrate."

Displaced Kurds stuck at a border after a Turkish offensive in northeastern Syria on October 21. Reuters

Trump downplayed the chain of events, which includes killings of Kurdish civilians. While Trump announced "a major breakthrough" in Turkish-Kurdish relations, the US and Turkey have contradicted each other on the definition of "cease-fire."

Despite the differences, Trump on Wednesday said he believed a "permanent" cease-fire would be achieved after talks with the leaders of the Kurdish-led Syrian Democratic Forces and Erdogan.

"Let someone else fight over this long-bloodstained sand," Trump said, adding that "we've saved the lives of many, many Kurds."

Trump also announced he would lift the sanctions he imposed on Turkey "unless something happens that we're not happy with."