Russian-backed Syrian fighters wasted no time capitalizing on the US withdrawal from Syria on Monday, deploying troops deep inside Kurdish territory south of the Turkish border less than 24 hours after Team Trump announced American forces would be leaving northern Syria.

Washington’s former Kurdish allies in the fight against ISIS said they invited in the government troops as an emergency step to help fend off an assault by Turkey, launched last week after President Trump moved US troops aside in what bitter Kurds called a betrayal.

Washington’s decision to abandon a policy it had pursued for five years was seen as a positive for Turkish President Recep Tayyip Erdogan.

The Syrian army deployment was a victory for Syrian President Bashar al-Assad and his ally Russia, giving them a foothold in the biggest remaining part of Syria that had been beyond their grasp while it was under Kurdish control.

They will now face Turkish armed forces along a new front line hundreds of miles long.

Syrian state media reported that troops had already entered Tel Tamer, a town on the strategically important M4 highway that runs east and west around 18 miles south of the frontier with Turkey.

State television later showed residents welcoming Syrian forces into the town of Ain Issa, which lies on another part of the highway, hundreds of miles away.

Ain Issa commands the northern approaches to Raqqa, former capital of the ISIS “caliphate,” which Kurdish fighters recaptured from the militants two years ago in one of the biggest victories of the US-led campaign.

Much of the M4 skirts the southern fringe of territory where Turkey aims to set up a “safe zone” inside Syria.

Turkey said it had seized part of the highway.

An official of the Kurdish-led Syrian Democratic Forces said clashes were ongoing.

The swift Syrian government deployments underscored how suddenly the strategy the US had pursued in Syria for the past five years had crumbled overnight.

Washington announced Sunday it was pulling out its entire force of about 1,000 troops, who had provided air support, ground assistance and training for Syrian Kurds against ISIS since 2014.

A US official said Monday a diplomatic team working to help stabilize territory captured from ISIS had already pulled out.

US troops were still on the ground, but early phases of their withdrawal had started, the official said.

Two other US officials have told Reuters the bulk of the US pullout could be completed within days.

Sunday’s announcement of the US retreat came just a week after Trump gave what the Kurds consider the go-ahead for Turkey to attack, by shifting US troops out of the way.

“After the Americans abandoned the region and gave the green light for the Turkish attack, we were forced to explore another option, which is talks with Damascus and Moscow to find a way out and thwart these Turkish attacks,” senior Kurdish official Badran Jia Kurd said.

Jia Kurd described the new arrangement with Assad’s forces as a “preliminary military agreement,” and said political aspects would be discussed later.

Ankara says it aims to defeat the Kurdish YPG militia, which it views as a terrorist group because of its links to Kurdish separatists in Turkey.

A “safe zone” would be set up in Syria to resettle refugees, 3.6 million of whom are in Turkey.

“We are determined to continue the operation until the end, without paying attention to threats,” Erdogan said in a speech during a visit to Azerbaijan.

“Our battle will continue until ultimate victory is achieved.”

The fighting has raised Western concerns that the Kurds would be unable to keep thousands of ISIS fighters in jail and tens of thousands of their family members in camps.

The region’s Kurdish-led administration said 785 ISIS-affiliated foreigners escaped a camp at Ain Issa over the weekend.

Trump tweeted Monday that the Kurds might be releasing ISIS prisoners deliberately to lure US troops back. Escaped fighters could be “easily recaptured by Turkey or European Nations from where many came, but they should move quickly,” Trump said.

Treasury Secretary Steven Mnuchin said Monday that sanctions against Turkey were ready and he just needs Trump to sign off on them.

“As I’ve said, the sanctions are ready to go,” Mnuchin told reporters.

“We’ll be updating the president this morning, and then when he makes the decision, we’ll activate. This is an evolving situation. We’re monitoring the situation carefully.”

The Trump administration said last Friday that it had authorized sanctions that would shut down Turkey’s economy if Erdogan’s forces target Kurdish fighters or allow ISIS captives to escape.

Trump earlier Monday heralded the impending penalties.

“Big sanctions on Turkey coming! Do people really think we should go to war with NATO Member Turkey? Never ending wars will end!” Trump wrote on Twitter.