"The Kurds fought with us, but were paid massive amounts of money and equipment to do so," Trump added.

President Donald Trump on Monday justified his decision to withdraw US troops from Turkey's border with Syria, saying the region would have to "figure the situation out" and that America needed to get out of "ridiculous Endless Wars."

The US withdrawal from key positions along Syria's northern border, announced late Sunday, marks a major policy shift and effectively abandons the Kurds, who were Washington's main ally in the years-old battle against the so-called Islamic State group.

"Turkey, Europe, Syria, Iran, Iraq, Russia and the Kurds will now have to figure the situation out, and what they want to do with the captured ISIS fighters in their 'neighborhood.'" Trump tweeted.

"The Kurds fought with us, but were paid massive amounts of money and equipment to do so," he added.

"They have been fighting Turkey for decades. I held off this fight for almost 3 years but it is time for us to get out of these ridiculous Endless Wars, many of them tribal, and bring our soldiers home.

"WE WILL FIGHT WHERE IT IS TO OUR BENEFIT, AND ONLY FIGHT TO WIN."

The US leader again insisted that "100% of the ISIS caliphate" had been defeated, but warned that the United States would "crush ISIS again if they come anywhere near us!"

The Syrian Democratic Forces (SDF), the Kurdish-led militia that controls much of northeastern Syria, said early Monday in a statement that "US forces withdrew from the border areas with Turkey."

On Sunday, the White House said in a readout of a call between Trump and Turkish President Recep Tayyip Erdogan that Ankara would "soon be moving forward with its long-planned operation into Northern Syria" -- and that US forces would "no longer be in the immediate area."