US President Donald Trump warned Turkey on Monday against going too far in Syria, one day after giving Ankara a green light to invade its southern neighbor and sparking panic among Washingtons Kurdish allies. The US pulled back 50 to 100 "special operators" from Syrias northern frontier, where they have served as a buffer between the Turkish military and the Kurdish-led Syrian Democratic Forces, after Trumps surprise announcement in advance of an expected operation ordered by Ankara. Trump’s stern words seemed to be aimed at placating critics who accused him of abandoning the Syrian Kurds, who were crucial in the years-long campaign to defeat ISIS, by pulling out US forces. The decision drew criticism from Democrats and a rare rebuke from some of Trump’s fellow Republicans in Congress, including Senate Majority Leader Mitch McConnell. "A precipitous withdrawal of US forces from Syria would only benefit Russia, Iran, and the Assad regime," said McConnell. "And it would increase the risk that ISIS and other terrorist groups regroup.” “As I have stated strongly before, and just to reiterate, if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the Economy of Turkey (I’ve done before!)” Trump tweeted. However Trump also said he wanted to end the US military presence in the region. "We want to bring our troops back home from these endless wars and were like a police force. Were not fighting. Were policing." A senior administration official denied Trump had given a "green light" to an invasion, which raised the threat that thousands of ISIS fighters that the Kurds hold prisoner could be freed amid a fresh conflict, reported AFP. "It appears the Turks are intent on some sort of military operation," the official said on grounds of anonymity, adding: "There will be no US armed forces involvement." A Trump administration official, briefing reporters on a conference call, said 50 US troops in the region that Turkey has targeted would be redeployed elsewhere in Syria “where they aren’t in the crossfire.” The United States has about 1,000 troops in Syria. Turkish President Recep Tayyip Erdogan said Monday that the operation could "come any night without warning," while Kurds in the area girded for fighting. "The prudent should prepare for war," said Mustefa Bozan, a 79-year-old shopkeeper in Ras al-Ain, where a contingent of US Special Forces had been until early Monday. The Kurds lead the SDF, who were essential in the US-led coalition that defeated the ISIS. Turkey regards Kurdish forces within the SDF as a terror threat because it maintains ties to Kurdish militants inside Turkey, and has vowed to crush them. Ankara says it wants to establish a "safe zone" on the Syrian side of the border where it could send back some of the 3.6 million refugees from the eight-year war.Pentagon warns of destabilization Trumps announcement appeared to have caught many US officials by surprise, and they spent Monday seeking to discourage Ankara from acting. Pentagon spokesman Jonathan Hoffman warned Turkey of destabilizing blowback to the region if it invades. "The Department of Defense made clear to Turkey -- as did the president -- that we do not endorse a Turkish operation in Northern Syria," he said. SDF spokesman Mustefa Bali said Washingtons decision "is about to ruin the trust and cooperation between the SDF and US." "As the Syrian Democratic Forces, we are determined to defend our land at all costs," the group said. A Turkish attack raised the specter of some 10,000 ISIS fighters currently held by the SDF being let loose if SDF soldiers have to battle Turkish troops. Around 2,000 of them are ISIS "foreign fighters", and Trump assailed US allies in Europe for not taking back their nationals. If they escape or are released, the could reconstitute the ISIS, less than one year after it was defeated and its "caliphate" disintegrated. Trump declared that it would be the responsibility of Turkey and other countries to deal with the ISIS prisoners. "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," he said, using another acronym for the jihadists. Fearing yet another chapter of bloodshed and mass displacement, the United Nations said it was "preparing for the worst." The European Union warned that civilians would once again bear the brunt of a military assault.